diff --git a/GHGEN/utils.go b/GHGEN/utils.go
index f04c1b0890..9a6a19be03 100644
--- a/GHGEN/utils.go
+++ b/GHGEN/utils.go
@@ -7,77 +7,77 @@ package main
 import (
 	"fmt"
 	"io"
-	"os"
 	"path/filepath"
 	"strings"
 
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 func newJob(w io.Writer, name, runsOn, needs string, permissions map[string]string) {
-	mustFprintf(w, "  %s:\n", name)
-	mustFprintf(w, "    runs-on: %s\n", runsOn)
+	must.Fprintf(w, "  %s:\n", name)
+	must.Fprintf(w, "    runs-on: %s\n", runsOn)
 	if needs != "" {
-		mustFprintf(w, "    needs: %s\n", needs)
+		must.Fprintf(w, "    needs: %s\n", needs)
 	}
 	if len(permissions) > 0 {
-		mustFprintf(w, "    permissions:\n")
+		must.Fprintf(w, "    permissions:\n")
 		for key, value := range permissions {
-			mustFprintf(w, "      %s: %s\n", key, value)
+			must.Fprintf(w, "      %s: %s\n", key, value)
 		}
 	}
-	mustFprintf(w, "    steps:\n")
+	must.Fprintf(w, "    steps:\n")
 }
 
 func newStepCheckout(w io.Writer) {
-	mustFprintf(w, "      - uses: actions/checkout@v2\n")
-	mustFprintf(w, "        with:\n")
-	mustFprintf(w, "          fetch-depth: 0\n")
-	mustFprintf(w, "\n")
+	must.Fprintf(w, "      - uses: actions/checkout@v2\n")
+	must.Fprintf(w, "        with:\n")
+	must.Fprintf(w, "          fetch-depth: 0\n")
+	must.Fprintf(w, "\n")
 }
 
 func newStepSetupGo(w io.Writer, cacheName string) {
-	mustFprintf(w, "      - name: Get GOVERSION content\n")
-	mustFprintf(w, "        id: goversion\n")
-	mustFprintf(w, "        run: echo ::set-output name=version::$(cat GOVERSION)\n")
-	mustFprintf(w, "      - uses: magnetikonline/action-golang-cache@v2\n")
-	mustFprintf(w, "        with:\n")
-	mustFprintf(w, "          go-version: \"${{ steps.goversion.outputs.version }}\"\n")
-	mustFprintf(w, "          cache-key-suffix: \"-%s-${{ steps.goversion.outputs.version }}\"\n", cacheName)
-	mustFprintf(w, "\n")
+	must.Fprintf(w, "      - name: Get GOVERSION content\n")
+	must.Fprintf(w, "        id: goversion\n")
+	must.Fprintf(w, "        run: echo ::set-output name=version::$(cat GOVERSION)\n")
+	must.Fprintf(w, "      - uses: magnetikonline/action-golang-cache@v2\n")
+	must.Fprintf(w, "        with:\n")
+	must.Fprintf(w, "          go-version: \"${{ steps.goversion.outputs.version }}\"\n")
+	must.Fprintf(w, "          cache-key-suffix: \"-%s-${{ steps.goversion.outputs.version }}\"\n", cacheName)
+	must.Fprintf(w, "\n")
 }
 
 func newStepSetupPsiphon(w io.Writer) {
-	mustFprintf(w, "      - run: |\n")
-	mustFprintf(w, "          echo -n $PSIPHON_CONFIG_KEY > ./internal/engine/psiphon-config.key\n")
-	mustFprintf(w, "          echo $PSIPHON_CONFIG_JSON_AGE_BASE64 | base64 -d > ./internal/engine/psiphon-config.json.age\n")
-	mustFprintf(w, "        env:\n")
-	mustFprintf(w, "          PSIPHON_CONFIG_KEY: ${{ secrets.PSIPHON_CONFIG_KEY }}\n")
-	mustFprintf(w, "          PSIPHON_CONFIG_JSON_AGE_BASE64: ${{ secrets.PSIPHON_CONFIG_JSON_AGE_BASE64 }}\n")
-	mustFprintf(w, "\n")
+	must.Fprintf(w, "      - run: |\n")
+	must.Fprintf(w, "          echo -n $PSIPHON_CONFIG_KEY > ./internal/engine/psiphon-config.key\n")
+	must.Fprintf(w, "          echo $PSIPHON_CONFIG_JSON_AGE_BASE64 | base64 -d > ./internal/engine/psiphon-config.json.age\n")
+	must.Fprintf(w, "        env:\n")
+	must.Fprintf(w, "          PSIPHON_CONFIG_KEY: ${{ secrets.PSIPHON_CONFIG_KEY }}\n")
+	must.Fprintf(w, "          PSIPHON_CONFIG_JSON_AGE_BASE64: ${{ secrets.PSIPHON_CONFIG_JSON_AGE_BASE64 }}\n")
+	must.Fprintf(w, "\n")
 }
 
 func newStepMake(w io.Writer, target string) {
-	mustFprintf(w, "      - run: make %s\n", target)
-	mustFprintf(w, "\n")
+	must.Fprintf(w, "      - run: make %s\n", target)
+	must.Fprintf(w, "\n")
 }
 
 func newStepUploadArtifacts(w io.Writer, artifacts []string) {
 	for _, arti := range artifacts {
-		mustFprintf(w, "      - uses: actions/upload-artifact@v2\n")
-		mustFprintf(w, "        with:\n")
-		mustFprintf(w, "          name: %s\n", filepath.Base(arti))
-		mustFprintf(w, "          path: %s\n", arti)
-		mustFprintf(w, "\n")
+		must.Fprintf(w, "      - uses: actions/upload-artifact@v2\n")
+		must.Fprintf(w, "        with:\n")
+		must.Fprintf(w, "          name: %s\n", filepath.Base(arti))
+		must.Fprintf(w, "          path: %s\n", arti)
+		must.Fprintf(w, "\n")
 	}
 }
 
 func newStepDownloadArtifacts(w io.Writer, artifacts []string) {
 	for _, arti := range artifacts {
-		mustFprintf(w, "      - uses: actions/download-artifact@v2\n")
-		mustFprintf(w, "        with:\n")
-		mustFprintf(w, "          name: %s\n", filepath.Base(arti))
-		mustFprintf(w, "\n")
+		must.Fprintf(w, "      - uses: actions/download-artifact@v2\n")
+		must.Fprintf(w, "        with:\n")
+		must.Fprintf(w, "          name: %s\n", filepath.Base(arti))
+		must.Fprintf(w, "\n")
 	}
 }
 
@@ -87,91 +87,80 @@ func newStepGHPublish(w io.Writer, artifacts []string) {
 	for _, arti := range artifacts {
 		artifactsNames = append(artifactsNames, filepath.Base(arti))
 	}
-	mustFprintf(w, "      - run: ./script/ghpublish.bash %s\n", strings.Join(artifactsNames, " "))
-	mustFprintf(w, "        env:\n")
-	mustFprintf(w, "          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}\n")
-	mustFprintf(w, "\n")
+	must.Fprintf(w, "      - run: ./script/ghpublish.bash %s\n", strings.Join(artifactsNames, " "))
+	must.Fprintf(w, "        env:\n")
+	must.Fprintf(w, "          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}\n")
+	must.Fprintf(w, "\n")
 }
 
 func newStepSetupLinuxDockerGoCache(w io.Writer, name string) {
-	mustFprintf(w, "      - uses: actions/cache@v3\n")
-	mustFprintf(w, "        with:\n")
-	mustFprintf(w, "          path: GOCACHE\n")
-	mustFprintf(w, "          key: linux-build-cache-%s\n", name)
-	mustFprintf(w, "\n")
+	must.Fprintf(w, "      - uses: actions/cache@v3\n")
+	must.Fprintf(w, "        with:\n")
+	must.Fprintf(w, "          path: GOCACHE\n")
+	must.Fprintf(w, "          key: linux-build-cache-%s\n", name)
+	must.Fprintf(w, "\n")
 
 }
 
 func newSetupInstallQemuUserStatic(w io.Writer) {
-	mustFprintf(w, "      - run: sudo apt-get update -q\n")
-	mustFprintf(w, "      - run: sudo apt-get install -y qemu-user-static\n")
-	mustFprintf(w, "\n")
+	must.Fprintf(w, "      - run: sudo apt-get update -q\n")
+	must.Fprintf(w, "      - run: sudo apt-get install -y qemu-user-static\n")
+	must.Fprintf(w, "\n")
 }
 
 func newStepInstallTor(w io.Writer) {
-	mustFprintf(w, "      - run: sudo apt-get update -q\n")
-	mustFprintf(w, "      - run: sudo apt-get install -y tor\n")
-	mustFprintf(w, "\n")
+	must.Fprintf(w, "      - run: sudo apt-get update -q\n")
+	must.Fprintf(w, "      - run: sudo apt-get install -y tor\n")
+	must.Fprintf(w, "\n")
 }
 
 func newStepRunOONIProbeIntegrationTests(w io.Writer, os, arch, ext string) {
 	executable := fmt.Sprintf("ooniprobe-%s-%s%s", os, arch, ext)
 	if os != "windows" {
-		mustFprintf(w, "      - run: chmod +x %s\n", executable)
+		must.Fprintf(w, "      - run: chmod +x %s\n", executable)
 	}
-	mustFprintf(w, "      - run: ./E2E/ooniprobe.bash ./%s\n", executable)
-	mustFprintf(w, "        shell: bash\n")
-	mustFprintf(w, "\n")
+	must.Fprintf(w, "      - run: ./E2E/ooniprobe.bash ./%s\n", executable)
+	must.Fprintf(w, "        shell: bash\n")
+	must.Fprintf(w, "\n")
 }
 
 func newStepRunMiniooniIntegrationTests(w io.Writer, os, arch, ext string) {
 	executable := fmt.Sprintf("miniooni-%s-%s%s", os, arch, ext)
 	if os != "windows" {
-		mustFprintf(w, "      - run: chmod +x %s\n", executable)
+		must.Fprintf(w, "      - run: chmod +x %s\n", executable)
 	}
-	mustFprintf(w, "      - run: ./E2E/miniooni.bash ./%s\n", executable)
-	mustFprintf(w, "        shell: bash\n")
-	mustFprintf(w, "\n")
+	must.Fprintf(w, "      - run: ./E2E/miniooni.bash ./%s\n", executable)
+	must.Fprintf(w, "        shell: bash\n")
+	must.Fprintf(w, "\n")
 }
 
 func newStepInstallMingwW64(w io.Writer) {
-	mustFprintf(w, "      - run: sudo apt-get update -q\n")
-	mustFprintf(w, "      - run: sudo apt-get install -y mingw-w64\n")
-	mustFprintf(w, "\n")
-}
-
-func mustFprintf(w io.Writer, format string, v ...any) {
-	_, err := fmt.Fprintf(w, format, v...)
-	runtimex.PanicOnError(err, "fmt.Fprintf failed")
-}
-
-func mustClose(c io.Closer) {
-	err := c.Close()
-	runtimex.PanicOnError(err, "c.Close failed")
+	must.Fprintf(w, "      - run: sudo apt-get update -q\n")
+	must.Fprintf(w, "      - run: sudo apt-get install -y mingw-w64\n")
+	must.Fprintf(w, "\n")
 }
 
 func generateWorkflowFile(name string, jobs []Job) {
 	filename := filepath.Join(".github", "workflows", name+".yml")
-	fp, err := os.Create(filename)
-	runtimex.PanicOnError(err, "os.Create failed")
-	defer mustClose(fp)
-	mustFprintf(fp, "# File generated by `go run ./GHGEN`; DO NOT EDIT.\n")
-	mustFprintf(fp, "\n")
-	mustFprintf(fp, "name: %s\n", name)
-	mustFprintf(fp, "on:\n")
-	mustFprintf(fp, "  push:\n")
-	mustFprintf(fp, "    branches:\n")
-	mustFprintf(fp, "      - \"release/**\"\n")
-	mustFprintf(fp, "      - \"fullbuild\"\n")
-	mustFprintf(fp, "      - \"%sbuild\"\n", name)
-	mustFprintf(fp, "    tags:\n")
-	mustFprintf(fp, "      - \"v*\"\n")
-	mustFprintf(fp, "  schedule:\n")
-	mustFprintf(fp, "    - cron: \"17 1 * * *\"\n")
-	mustFprintf(fp, "\n")
-	mustFprintf(fp, "jobs:\n")
+	fp := must.CreateFile(filename)
+	defer fp.MustClose()
+	must.Fprintf(fp, "# File generated by `go run ./GHGEN`; DO NOT EDIT.\n")
+	must.Fprintf(fp, "\n")
+	must.Fprintf(fp, "name: %s\n", name)
+	must.Fprintf(fp, "on:\n")
+	must.Fprintf(fp, "  push:\n")
+	must.Fprintf(fp, "    branches:\n")
+	must.Fprintf(fp, "      - \"release/**\"\n")
+	must.Fprintf(fp, "      - \"fullbuild\"\n")
+	must.Fprintf(fp, "      - \"%sbuild\"\n", name)
+	must.Fprintf(fp, "    tags:\n")
+	must.Fprintf(fp, "      - \"v*\"\n")
+	must.Fprintf(fp, "  schedule:\n")
+	must.Fprintf(fp, "    - cron: \"17 1 * * *\"\n")
+	must.Fprintf(fp, "\n")
+	must.Fprintf(fp, "jobs:\n")
 	for _, job := range jobs {
 		job.Action(fp, &job)
 	}
-	mustFprintf(fp, "# End of autogenerated file\n")
+	must.Fprintf(fp, "# End of autogenerated file\n")
 }
diff --git a/internal/cmd/miniooni/session.go b/internal/cmd/miniooni/session.go
index a56262c02b..1bef28ce70 100644
--- a/internal/cmd/miniooni/session.go
+++ b/internal/cmd/miniooni/session.go
@@ -10,6 +10,7 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/engine"
 	"github.com/ooni/probe-cli/v3/internal/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 	"github.com/ooni/probe-cli/v3/internal/version"
 )
@@ -24,7 +25,7 @@ func newSessionOrPanic(ctx context.Context, currentOptions *Options,
 	miniooniDir string, logger model.Logger) *engine.Session {
 	var proxyURL *url.URL
 	if currentOptions.Proxy != "" {
-		proxyURL = mustParseURL(currentOptions.Proxy)
+		proxyURL = must.ParseURL(currentOptions.Proxy)
 	}
 
 	kvstore2dir := filepath.Join(miniooniDir, "kvstore2")
diff --git a/internal/cmd/miniooni/utils.go b/internal/cmd/miniooni/utils.go
index cb51e13398..ac0c4f5294 100644
--- a/internal/cmd/miniooni/utils.go
+++ b/internal/cmd/miniooni/utils.go
@@ -6,7 +6,6 @@ package main
 
 import (
 	"errors"
-	"net/url"
 	"os"
 	"runtime"
 	"strings"
@@ -54,13 +53,6 @@ func mustMakeMapStringAny(input []string) (output map[string]any) {
 	return
 }
 
-// mustParseURL parses the given URL or panics
-func mustParseURL(URL string) *url.URL {
-	rv, err := url.Parse(URL)
-	runtimex.PanicOnError(err, "cannot parse URL")
-	return rv
-}
-
 // gethomedir returns the home directory. If optionsHome is set, then we
 // return that string as the home directory. Otherwise, we use typical
 // platform-specific environment variables to determine the home. In case
diff --git a/internal/cmd/oohelper/internal/client.go b/internal/cmd/oohelper/internal/client.go
index f175d5cb4e..bdf47beaec 100644
--- a/internal/cmd/oohelper/internal/client.go
+++ b/internal/cmd/oohelper/internal/client.go
@@ -12,8 +12,8 @@ import (
 
 	"github.com/apex/log"
 	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
 	"github.com/ooni/probe-cli/v3/internal/version"
 )
 
@@ -110,8 +110,7 @@ func (oo OOClient) Do(ctx context.Context, config OOConfig) (*CtrlResponse, erro
 		},
 		TCPConnect: endpoints,
 	}
-	data, err := json.Marshal(creq)
-	runtimex.PanicOnError(err, "oohelper: cannot marshal control request")
+	data := must.MarshalJSON(creq)
 	log.Debugf("out: %s", string(data))
 	req, err := http.NewRequestWithContext(ctx, "POST", config.ServerURL, bytes.NewReader(data))
 	if err != nil {
diff --git a/internal/cmd/oohelper/oohelper.go b/internal/cmd/oohelper/oohelper.go
index 132194c6de..e946d0e0d6 100644
--- a/internal/cmd/oohelper/oohelper.go
+++ b/internal/cmd/oohelper/oohelper.go
@@ -4,13 +4,13 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
 
 	"github.com/apex/log"
 	"github.com/ooni/probe-cli/v3/internal/cmd/oohelper/internal"
 	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
@@ -41,8 +41,7 @@ func main() {
 	flag.Parse()
 	log.SetLevel(logmap[*debug])
 	cresp := wcth()
-	data, err := json.MarshalIndent(cresp, "", "    ")
-	runtimex.PanicOnError(err, "json.MarshalIndent failed")
+	data := must.MarshalAndIndentJSON(cresp, "", "    ")
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/cmd/oohelperd/handler.go b/internal/cmd/oohelperd/handler.go
index 2e186ac708..f8e2a46acb 100644
--- a/internal/cmd/oohelperd/handler.go
+++ b/internal/cmd/oohelperd/handler.go
@@ -13,8 +13,8 @@ import (
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
 	"github.com/ooni/probe-cli/v3/internal/version"
 )
 
@@ -87,8 +87,7 @@ func (h *handler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 	metricRequestsCount.WithLabelValues("200", "ok").Inc()
 	// We assume that the following call cannot fail because it's a
 	// clearly-serializable data structure.
-	data, err = json.Marshal(cresp)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data = must.MarshalJSON(cresp)
 	w.Header().Add("Content-Type", "application/json")
 	w.Write(data)
 }
diff --git a/internal/cmd/oohelperd/main.go b/internal/cmd/oohelperd/main.go
index 3e97b9d3a9..84f0cebb86 100644
--- a/internal/cmd/oohelperd/main.go
+++ b/internal/cmd/oohelperd/main.go
@@ -4,7 +4,6 @@ package main
 import (
 	"context"
 	"flag"
-	"net"
 	"net/http"
 	"sync"
 	"sync/atomic"
@@ -12,8 +11,8 @@ import (
 
 	"github.com/apex/log"
 	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
@@ -103,8 +102,7 @@ func main() {
 		},
 	})
 	srv := &http.Server{Addr: *endpoint, Handler: mux}
-	listener, err := net.Listen("tcp", *endpoint)
-	runtimex.PanicOnError(err, "net.Listen failed")
+	listener := must.Listen("tcp", *endpoint)
 	srvAddr <- listener.Addr().String()
 	srvWg.Add(1)
 	go srv.Serve(listener)
diff --git a/internal/cmd/oohelperd/main_test.go b/internal/cmd/oohelperd/main_test.go
index 001a68460e..9d392bd2b7 100644
--- a/internal/cmd/oohelperd/main_test.go
+++ b/internal/cmd/oohelperd/main_test.go
@@ -10,8 +10,8 @@ import (
 	"testing"
 
 	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 func TestMainWorkingAsIntended(t *testing.T) {
@@ -34,8 +34,7 @@ func TestMainWorkingAsIntended(t *testing.T) {
 			"8.8.4.4:443",
 		},
 	}
-	data, err := json.Marshal(jsonReq)
-	runtimex.PanicOnError(err, "cannot marshal request")
+	data := must.MarshalJSON(jsonReq)
 
 	// construct the test helper's URL
 	endpoint := <-srvAddr
@@ -44,8 +43,7 @@ func TestMainWorkingAsIntended(t *testing.T) {
 		Host:   endpoint,
 		Path:   "/",
 	}
-	req, err := http.NewRequest("POST", URL.String(), bytes.NewReader(data))
-	runtimex.PanicOnError(err, "cannot create new HTTP request")
+	req := must.NewHTTPRequest("POST", URL.String(), bytes.NewReader(data))
 
 	// issue the request and get the response
 	resp, err := http.DefaultClient.Do(req)
diff --git a/internal/cmd/oonireport/oonireport.go b/internal/cmd/oonireport/oonireport.go
index 80dddb45ad..b0f20f604e 100644
--- a/internal/cmd/oonireport/oonireport.go
+++ b/internal/cmd/oonireport/oonireport.go
@@ -4,7 +4,6 @@ package main
 import (
 	"bufio"
 	"context"
-	"encoding/json"
 	"fmt"
 	"io"
 	"os"
@@ -14,6 +13,7 @@ import (
 
 	"github.com/ooni/probe-cli/v3/internal/engine"
 	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/probeservices"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 	"github.com/ooni/probe-cli/v3/internal/version"
@@ -59,9 +59,8 @@ func canOpen(filepath string) bool {
 
 func readLines(path string) []string {
 	// open measurement file
-	file, err := os.Open(path)
-	runtimex.PanicOnError(err, "Open file error.")
-	defer file.Close()
+	file := must.OpenFile(path)
+	defer file.MustClose()
 
 	scanner := bufio.NewScanner(file)
 	// the maximum line length should be selected really big
@@ -103,8 +102,7 @@ func newSubmitter(sess *engine.Session, ctx context.Context) *probeservices.Subm
 // toMeasurement loads an input string as model.Measurement
 func toMeasurement(s string) *model.Measurement {
 	var mm model.Measurement
-	err := json.Unmarshal([]byte(s), &mm)
-	runtimex.PanicOnError(err, "json.Unmarshal error")
+	must.UnmarshalJSON([]byte(s), &mm)
 	return &mm
 }
 
diff --git a/internal/cmd/ooporthelper/main.go b/internal/cmd/ooporthelper/main.go
index 55b77f0e64..9d0d345e14 100644
--- a/internal/cmd/ooporthelper/main.go
+++ b/internal/cmd/ooporthelper/main.go
@@ -10,7 +10,7 @@ import (
 
 	"github.com/apex/log"
 	"github.com/ooni/probe-cli/v3/internal/experiment/portfiltering"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 var (
@@ -41,8 +41,7 @@ func handleConnection(ctx context.Context, conn net.Conn) {
 func listenTCP(ctx context.Context, port string) {
 	defer srvWg.Done()
 	address := net.JoinHostPort("127.0.0.1", port)
-	listener, err := net.Listen("tcp", address)
-	runtimex.PanicOnError(err, "net.Listen failed")
+	listener := must.Listen("tcp", address)
 	go shutdown(ctx, listener)
 	srvTestChan <- port // send to channel to imply server will start listening on port
 	for {
diff --git a/internal/database/database_test.go b/internal/database/database_test.go
index 355471c078..146cfbc980 100644
--- a/internal/database/database_test.go
+++ b/internal/database/database_test.go
@@ -4,8 +4,6 @@ import (
 	"io/ioutil"
 	"os"
 	"testing"
-
-	"github.com/apex/log"
 )
 
 func TestConnect(t *testing.T) {
@@ -26,7 +24,6 @@ func TestConnect(t *testing.T) {
 	}
 
 	if len(colls) < 1 {
-		log.Fatal("missing tables")
+		t.Fatal("missing tables")
 	}
-
 }
diff --git a/internal/engine/checkincache.go b/internal/engine/checkincache.go
index 0e7e09e854..4960ac4228 100644
--- a/internal/engine/checkincache.go
+++ b/internal/engine/checkincache.go
@@ -9,7 +9,7 @@ import (
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/model"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 // checkInFlagsState is the state created by check-in flags.
@@ -33,8 +33,7 @@ func (s *Session) updateCheckInFlagsState(resp *model.OOAPICheckInResult) error
 		Expire: time.Now().Add(24 * time.Hour),
 		Flags:  resp.Conf.Features,
 	}
-	data, err := json.Marshal(wrapper)
-	runtimex.PanicOnError(err, "json.Marshal unexpectedly failed")
+	data := must.MarshalJSON(wrapper)
 	return s.kvStore.Set(checkInFlagsState, data)
 }
 
diff --git a/internal/experiment/dnscheck/dnscheck.go b/internal/experiment/dnscheck/dnscheck.go
index 5979861bd3..39d784a147 100644
--- a/internal/experiment/dnscheck/dnscheck.go
+++ b/internal/experiment/dnscheck/dnscheck.go
@@ -17,7 +17,7 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/experiment/urlgetter"
 	"github.com/ooni/probe-cli/v3/internal/legacy/netx"
 	"github.com/ooni/probe-cli/v3/internal/model"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/tracex"
 )
 
@@ -291,10 +291,9 @@ func makeResolverURL(URL *url.URL, addr string) string {
 	}
 	// 2. adjust hostname if we also have a port
 	if hasPort := URL.Port() != ""; hasPort {
-		_, port, err := net.SplitHostPort(URL.Host)
 		// We say this cannot fail because we already parsed the URL to validate
 		// its scheme and hence the URL hostname should be well formed.
-		runtimex.PanicOnError(err, "net.SplitHostPort should not fail here")
+		_, port := must.SplitHostPort(URL.Host)
 		hostname = net.JoinHostPort(hostname, port)
 	} else if idx := strings.Index(addr, ":"); idx >= 0 {
 		// Make sure an IPv6 address hostname without a port is properly
diff --git a/internal/experiment/dnsping/dnsping_test.go b/internal/experiment/dnsping/dnsping_test.go
index bc03bea34d..9b6b80a6e9 100644
--- a/internal/experiment/dnsping/dnsping_test.go
+++ b/internal/experiment/dnsping/dnsping_test.go
@@ -3,7 +3,6 @@ package dnsping
 import (
 	"context"
 	"errors"
-	"log"
 	"net"
 	"net/url"
 	"testing"
@@ -101,7 +100,7 @@ func TestMeasurer_run(t *testing.T) {
 	t.Run("with local listener", func(t *testing.T) {
 		srvrURL, dnsListener, err := startDNSServer()
 		if err != nil {
-			log.Fatal(err)
+			t.Fatal(err)
 		}
 		defer dnsListener.Close()
 		meas, m, err := runHelper(srvrURL)
diff --git a/internal/experiment/simplequicping/simplequicping_test.go b/internal/experiment/simplequicping/simplequicping_test.go
index 808d21ca9c..f4c3b118e7 100644
--- a/internal/experiment/simplequicping/simplequicping_test.go
+++ b/internal/experiment/simplequicping/simplequicping_test.go
@@ -8,7 +8,6 @@ import (
 	"crypto/x509"
 	"encoding/pem"
 	"errors"
-	"log"
 	"math/big"
 	"net/url"
 	"testing"
@@ -105,7 +104,7 @@ func TestMeasurer_run(t *testing.T) {
 	t.Run("with local listener", func(t *testing.T) {
 		srvrURL, listener, err := startEchoServer()
 		if err != nil {
-			log.Fatal(err)
+			t.Fatal(err)
 		}
 		defer listener.Close()
 		meas, m, err := runHelper(srvrURL)
diff --git a/internal/experiment/tlsmiddlebox/conn_test.go b/internal/experiment/tlsmiddlebox/conn_test.go
index 364688fc12..9b043ea681 100644
--- a/internal/experiment/tlsmiddlebox/conn_test.go
+++ b/internal/experiment/tlsmiddlebox/conn_test.go
@@ -6,13 +6,12 @@ import (
 	"io"
 	"net/http"
 	"net/http/httptest"
-	"net/url"
 	"syscall"
 	"testing"
 
 	"github.com/ooni/probe-cli/v3/internal/model/mocks"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 func TestDialerTTLWrapperConn(t *testing.T) {
@@ -143,8 +142,7 @@ func TestGetSoErr(t *testing.T) {
 			w.WriteHeader(200)
 		}))
 		defer srvr.Close()
-		URL, err := url.Parse(srvr.URL)
-		runtimex.PanicOnError(err, "url.Parse failed")
+		URL := must.ParseURL(srvr.URL)
 		d := NewDialerTTLWrapper()
 		ctx := context.Background()
 		conn, err := d.DialContext(ctx, "tcp", URL.Host)
diff --git a/internal/experiment/tor/tor.go b/internal/experiment/tor/tor.go
index 11fe42cbae..ee2e2f7ae4 100644
--- a/internal/experiment/tor/tor.go
+++ b/internal/experiment/tor/tor.go
@@ -5,7 +5,6 @@ package tor
 
 import (
 	"context"
-	"encoding/json"
 	"errors"
 	"fmt"
 	"net/url"
@@ -15,6 +14,7 @@ import (
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
 	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 	"github.com/ooni/probe-cli/v3/internal/scrubber"
@@ -270,15 +270,13 @@ func maybeSanitize(input TargetResults, kt keytarget) TargetResults {
 	if !kt.private() {
 		return input
 	}
-	data, err := json.Marshal(input)
-	runtimex.PanicOnError(err, "json.Marshal should not fail here")
+	data := must.MarshalJSON(input)
 	// Implementation note: here we are using a strict scrubbing policy where
 	// we remove all IP _endpoints_, mainly for convenience, because we already
 	// have a well tested implementation that does that.
 	data = []byte(scrubber.Scrub(string(data)))
 	var out TargetResults
-	err = json.Unmarshal(data, &out)
-	runtimex.PanicOnError(err, "json.Unmarshal should not fail here")
+	must.UnmarshalJSON(data, &out)
 	return out
 }
 
diff --git a/internal/experiment/urlgetter/runner.go b/internal/experiment/urlgetter/runner.go
index 825160754d..8ea656123e 100644
--- a/internal/experiment/urlgetter/runner.go
+++ b/internal/experiment/urlgetter/runner.go
@@ -11,6 +11,7 @@ import (
 
 	"github.com/ooni/probe-cli/v3/internal/legacy/netx"
 	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
@@ -62,8 +63,7 @@ func MaybeUserAgent(ua string) string {
 
 func (r Runner) httpGet(ctx context.Context, url string) error {
 	// Implementation note: empty Method implies using the GET method
-	req, err := http.NewRequest(r.Config.Method, url, nil)
-	runtimex.PanicOnError(err, "http.NewRequest failed")
+	req := must.NewHTTPRequest(r.Config.Method, url, nil)
 	req = req.WithContext(ctx)
 	req.Header.Set("Accept", model.HTTPHeaderAccept)
 	req.Header.Set("Accept-Language", model.HTTPHeaderAcceptLanguage)
diff --git a/internal/experiment/webconnectivity/endpoints.go b/internal/experiment/webconnectivity/endpoints.go
index ac7d072745..6ca9021a1b 100644
--- a/internal/experiment/webconnectivity/endpoints.go
+++ b/internal/experiment/webconnectivity/endpoints.go
@@ -4,7 +4,7 @@ import (
 	"net"
 	"net/url"
 
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 // EndpointInfo describes a TCP/TLS endpoint.
@@ -69,8 +69,7 @@ func NewEndpointPort(URL *url.URL) (out EndpointPort) {
 		out.URLGetterScheme, out.Port = "tlshandshake", "443"
 	}
 	if URL.Host != URL.Hostname() {
-		_, port, err := net.SplitHostPort(URL.Host)
-		runtimex.PanicOnError(err, "SplitHostPort should not fail here")
+		_, port := must.SplitHostPort(URL.Host)
 		out.Port = port
 	}
 	return
diff --git a/internal/experiment/webconnectivitylte/priority.go b/internal/experiment/webconnectivitylte/priority.go
index c86a4cce90..50814eccc1 100644
--- a/internal/experiment/webconnectivitylte/priority.go
+++ b/internal/experiment/webconnectivitylte/priority.go
@@ -30,10 +30,10 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"net"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
@@ -126,8 +126,7 @@ func (ps *prioritySelector) log(format string, v ...any) {
 // permissionToFetch returns whether this ready-to-use connection
 // is permitted to perform a round trip and fetch the webpage.
 func (ps *prioritySelector) permissionToFetch(address string) bool {
-	ipAddr, _, err := net.SplitHostPort(address)
-	runtimex.PanicOnError(err, "net.SplitHostPort failed")
+	ipAddr, _ := must.SplitHostPort(address)
 	r := &priorityRequest{
 		addr: ipAddr,
 		resp: make(chan bool, 1), // buffer to simplify selector() implementation
diff --git a/internal/experiment/whatsapp/whatsapp.go b/internal/experiment/whatsapp/whatsapp.go
index 94055b07dd..8a3cab1777 100644
--- a/internal/experiment/whatsapp/whatsapp.go
+++ b/internal/experiment/whatsapp/whatsapp.go
@@ -8,13 +8,12 @@ import (
 	"errors"
 	"fmt"
 	"math/rand"
-	"net/url"
 	"regexp"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/experiment/urlgetter"
 	"github.com/ooni/probe-cli/v3/internal/model"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 const (
@@ -74,8 +73,7 @@ func (tk *TestKeys) Update(v urlgetter.MultiOutput) {
 	// Set the status of WhatsApp endpoints
 	if endpointPattern.MatchString(v.Input.Target) {
 		if v.TestKeys.Failure != nil {
-			parsed, err := url.Parse(v.Input.Target)
-			runtimex.PanicOnError(err, "url.Parse should not fail here")
+			parsed := must.ParseURL(v.Input.Target)
 			hostname := parsed.Hostname()
 			tk.WhatsappEndpointsCount[hostname]++
 			// Implementation note: here we're counting twice because we test each
diff --git a/internal/geoipx/geoipx.go b/internal/geoipx/geoipx.go
index 5640e8b3fd..2c54b34f2a 100644
--- a/internal/geoipx/geoipx.go
+++ b/internal/geoipx/geoipx.go
@@ -34,7 +34,7 @@ func LookupASN(ip string) (asn uint, org string, err error) {
 func LookupCC(ip string) (cc string, err error) {
 	cc = model.DefaultProbeCC
 	db, err := maxminddb.FromBytes(assets.OOMMDBDatabaseBytes)
-	runtimex.PanicOnError(err, "cannot load embedded geoip2 country database")
+	runtimex.PanicOnError(err, "cannot load embedded geoip2 database")
 	defer db.Close()
 	record, err := assets.OOMMDBLooup(db, net.ParseIP(ip))
 	if err != nil {
diff --git a/internal/model/measurement.go b/internal/model/measurement.go
index 7cd2a8e13e..03b36b3328 100644
--- a/internal/model/measurement.go
+++ b/internal/model/measurement.go
@@ -12,7 +12,7 @@ import (
 	"net"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 const (
@@ -198,8 +198,7 @@ var scrubJSONUnmarshalTopLevelKeys = json.Unmarshal
 // scrubTopLevelKeys removes [currentIP] from the top-level keys
 // of [m] by rewriting these keys in place.
 func scrubTopLevelKeys(m *Measurement, currentIP string) error {
-	data, err := json.Marshal(m)
-	runtimex.PanicOnError(err, "json.Marshal(m) failed") // m must serialize
+	data := must.MarshalJSON(m)
 	data = bytes.ReplaceAll(data, []byte(currentIP), []byte(Scrubbed))
 	return scrubJSONUnmarshalTopLevelKeys(data, &m)
 }
@@ -210,8 +209,7 @@ var scrubJSONUnmarshalTestKeys = json.Unmarshal
 // scrubTestKeys removes [currentIP] from the TestKeys by rewriting
 // them in place while preserving their original type
 func scrubTestKeys(m *Measurement, currentIP string) error {
-	data, err := json.Marshal(m.TestKeys)
-	runtimex.PanicOnError(err, "json.Marshal(m.TestKeys) failed") // m.TestKeys must serialize
+	data := must.MarshalJSON(m.TestKeys)
 	data = bytes.ReplaceAll(data, []byte(currentIP), []byte(Scrubbed))
 	return scrubJSONUnmarshalTestKeys(data, &m.TestKeys)
 }
diff --git a/internal/must/must.go b/internal/must/must.go
new file mode 100644
index 0000000000..fcd8fd2655
--- /dev/null
+++ b/internal/must/must.go
@@ -0,0 +1,104 @@
+// Package must contains functions that panic on error.
+package must
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/url"
+	"os"
+
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
+)
+
+// CreateFile is like [os.Create] but calls
+// [runtimex.PanicOnError] on failure.
+func CreateFile(name string) *File {
+	fp, err := os.Create(name)
+	runtimex.PanicOnError(err, "os.Create failed")
+	return &File{fp}
+}
+
+// OpenFile is like [os.Open] but calls
+// [runtimex.PanicOnError] on failure.
+func OpenFile(name string) *File {
+	fp, err := os.Open(name)
+	runtimex.PanicOnError(err, "os.Open failed")
+	return &File{fp}
+}
+
+// File wraps [os.File].
+type File struct {
+	*os.File
+}
+
+// MustClose is like [os.File.Close] but calls
+// [runtimex.PanicOnError] on failure.
+func (fp *File) MustClose() {
+	err := fp.File.Close()
+	runtimex.PanicOnError(err, "fp.File.Close failed")
+}
+
+// Fprintf is like [fmt.Fprintf] but calls
+// [runtimex.PanicOnError] on failure.
+func Fprintf(w io.Writer, format string, v ...any) {
+	_, err := fmt.Fprintf(w, format, v...)
+	runtimex.PanicOnError(err, "fmt.Fprintf failed")
+}
+
+// ParseURL is like [url.Parse] but calls
+// [runtimex.PanicOnError] on failure.
+func ParseURL(URL string) *url.URL {
+	parsed, err := url.Parse(URL)
+	runtimex.PanicOnError(err, "url.Parse failed")
+	return parsed
+}
+
+// MarshalJSON is like [json.Marshal] but calls
+// [runtimex.PanicOnError] on failure.
+func MarshalJSON(v any) []byte {
+	data, err := json.Marshal(v)
+	runtimex.PanicOnError(err, "json.Marshal failed")
+	return data
+}
+
+// MarshalAndIndentJSON is like [json.MarshalIndent] but calls
+// [runtimex.PanicOnError] on failure.
+func MarshalAndIndentJSON(v any, prefix string, indent string) []byte {
+	data, err := json.MarshalIndent(v, prefix, indent)
+	runtimex.PanicOnError(err, "json.MarshalIndent failed")
+	return data
+}
+
+// UnmarshalJSON is like [json.Marshal] but calls
+// [runtimex.PanicOnError] on failure.
+func UnmarshalJSON(data []byte, v any) {
+	err := json.Unmarshal(data, v)
+	runtimex.PanicOnError(err, "json.Unmarshal failed")
+}
+
+// Listen is like [net.Listen] but calls
+// [runtimex.PanicOnError] on failure.
+func Listen(network string, address string) net.Listener {
+	listener, err := net.Listen(network, address)
+	runtimex.PanicOnError(err, "net.Listen failed")
+	return listener
+}
+
+// NewHTTPRequest is like [http.NewRequest] but calls
+// [runtimex.PanicOnError] on failure.
+func NewHTTPRequest(method string, url string, body io.Reader) *http.Request {
+	req, err := http.NewRequest(method, url, body)
+	runtimex.PanicOnError(err, "http.NewRequest failed")
+	return req
+}
+
+// SplitHostPort is like [net.SplitHostPort] but calls
+// [runtimex.PanicOnError] on failure.
+func SplitHostPort(hostport string) (host string, port string) {
+	host, port, err := net.SplitHostPort(hostport)
+	runtimex.PanicOnError(err, "net.SplitHostPort failed")
+	return host, port
+}
diff --git a/internal/must/must_test.go b/internal/must/must_test.go
new file mode 100644
index 0000000000..ff20a7eb6e
--- /dev/null
+++ b/internal/must/must_test.go
@@ -0,0 +1,110 @@
+package must
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func TestCreateFile(t *testing.T) {
+	filename := filepath.Join("testdata", "test.txt")
+	filep := CreateFile(filename)
+	if _, err := filep.WriteString("antani"); err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(filename)
+	filep.MustClose()
+	data, err := os.ReadFile(filename)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(data) != "antani" {
+		t.Fatal("did not write the expected content")
+	}
+}
+
+func TestOpenFile(t *testing.T) {
+	filename := filepath.Join("testdata", ".gitignore")
+	filep := OpenFile(filename)
+	data, err := io.ReadAll(filep)
+	if err != nil {
+		t.Fatal(err)
+	}
+	filep.MustClose()
+	if string(data) != "*\n" && string(data) != "*\r\n" {
+		t.Fatal("unexpected content")
+	}
+}
+
+func TestFprintf(t *testing.T) {
+	w := &bytes.Buffer{}
+	Fprintf(w, "hello %s", "world")
+	if w.String() != "hello world" {
+		t.Fatal("unexpected buffer content")
+	}
+}
+
+func TestParseURL(t *testing.T) {
+	URL := ParseURL("https://www.google.com/")
+	if URL.Scheme != "https" || URL.Host != "www.google.com" || URL.Path != "/" {
+		t.Fatal("unexpected parsed URL")
+	}
+}
+
+func TestMarshalJSON(t *testing.T) {
+	data := MarshalJSON("foobar")
+	if string(data) != "\"foobar\"" {
+		t.Fatal("incorrect marshalling")
+	}
+}
+
+type example struct {
+	Name string
+	Age  int
+}
+
+func TestMarshalAndIndentJSON(t *testing.T) {
+	input := &example{Name: "sbs", Age: 40}
+	data := MarshalAndIndentJSON(input, "", "    ")
+	expected := []byte("{\n    \"Name\": \"sbs\",\n    \"Age\": 40\n}")
+	if diff := cmp.Diff(expected, data); diff != "" {
+		t.Fatal(diff)
+	}
+}
+
+func TestUnmarshalJSON(t *testing.T) {
+	input := []byte("{\n    \"Name\": \"sbs\",\n    \"Age\": 40\n}")
+	var entry example
+	UnmarshalJSON(input, &entry)
+	if entry.Name != "sbs" || entry.Age != 40 {
+		t.Fatal("did not unmarshal correctly")
+	}
+}
+
+func TestListen(t *testing.T) {
+	conn := Listen("tcp", "127.0.0.1:0")
+	// TODO(bassosimone): unclear to me what to test here?
+	conn.Close()
+}
+
+func TestNewHTTPRequest(t *testing.T) {
+	req := NewHTTPRequest("GET", "https://www.google.com/", nil)
+	if req.Method != "GET" {
+		t.Fatal("invalid method")
+	}
+	URL := req.URL
+	if URL.Scheme != "https" || URL.Host != "www.google.com" || URL.Path != "/" {
+		t.Fatal("unexpected parsed URL")
+	}
+}
+
+func TestSplitHostPort(t *testing.T) {
+	addr, port := SplitHostPort("127.0.0.1:8080")
+	if addr != "127.0.0.1" || port != "8080" {
+		t.Fatal("unexpected result")
+	}
+}
diff --git a/internal/must/testdata/.gitignore b/internal/must/testdata/.gitignore
new file mode 100644
index 0000000000..72e8ffc0db
--- /dev/null
+++ b/internal/must/testdata/.gitignore
@@ -0,0 +1 @@
+*
diff --git a/internal/netxlite/filtering/http.go b/internal/netxlite/filtering/http.go
index 031a0ea5bc..403bd8e59f 100644
--- a/internal/netxlite/filtering/http.go
+++ b/internal/netxlite/filtering/http.go
@@ -11,6 +11,7 @@ import (
 
 	"github.com/google/martian/v3/mitm"
 	"github.com/miekg/dns"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
@@ -89,8 +90,7 @@ func (p *HTTPServer) TLSConfig() *tls.Config {
 
 // newHTTPOrHTTPSServer is an internal factory for creating a new instance.
 func newHTTPOrHTTPSServer(action HTTPAction, enableTLS bool) *HTTPServer {
-	listener, err := net.Listen("tcp", "127.0.0.1:0")
-	runtimex.PanicOnError(err, "net.Listen failed")
+	listener := must.Listen("tcp", "127.0.0.1:0")
 	srv := &HTTPServer{
 		action:  action,
 		cert:    nil,
diff --git a/internal/netxlite/filtering/http_test.go b/internal/netxlite/filtering/http_test.go
index a2e297524f..9ee9261cce 100644
--- a/internal/netxlite/filtering/http_test.go
+++ b/internal/netxlite/filtering/http_test.go
@@ -30,7 +30,7 @@ func TestHTTPServer(t *testing.T) {
 		clnt := &http.Client{Transport: txp}
 		req, err := http.NewRequestWithContext(
 			ctx, method, URL.String(), bytes.NewReader(requestBody))
-		runtimex.PanicOnError(err, "http.NewRequest failed")
+		runtimex.PanicOnError(err, "http.NewRequestWithContext failed")
 		req.Host = host
 		return clnt.Do(req)
 	}
diff --git a/internal/netxlite/filtering/tls.go b/internal/netxlite/filtering/tls.go
index af6210a897..dc64d62e52 100644
--- a/internal/netxlite/filtering/tls.go
+++ b/internal/netxlite/filtering/tls.go
@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/google/martian/v3/mitm"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
@@ -79,8 +80,7 @@ func tlsConfigMITM() (*x509.Certificate, *rsa.PrivateKey, *mitm.Config) {
 func NewTLSServer(action TLSAction) *TLSServer {
 	done := make(chan bool)
 	cert, privkey, config := tlsConfigMITM()
-	listener, err := net.Listen("tcp", "127.0.0.1:0")
-	runtimex.PanicOnError(err, "net.Listen failed")
+	listener := must.Listen("tcp", "127.0.0.1:0")
 	ctx, cancel := context.WithCancel(context.Background())
 	endpoint := listener.Addr().String()
 	server := &TLSServer{
diff --git a/internal/netxlite/quic_test.go b/internal/netxlite/quic_test.go
index 5ccb888660..6fd74d045c 100644
--- a/internal/netxlite/quic_test.go
+++ b/internal/netxlite/quic_test.go
@@ -217,7 +217,7 @@ func TestQUICDialerQUICGo(t *testing.T) {
 				t.Fatal("not the error we expected", err)
 			}
 			if qconn != nil {
-				log.Fatal("expected nil connection here")
+				t.Fatal("expected nil connection here")
 			}
 		})
 
diff --git a/internal/ooapi/checkin.go b/internal/ooapi/checkin.go
index 89753280fe..b897660ff7 100644
--- a/internal/ooapi/checkin.go
+++ b/internal/ooapi/checkin.go
@@ -5,12 +5,11 @@ package ooapi
 //
 
 import (
-	"encoding/json"
 	"net/http"
 
 	"github.com/ooni/probe-cli/v3/internal/httpapi"
 	"github.com/ooni/probe-cli/v3/internal/model"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 // NewDescriptorCheckIn creates a new [httpapi.Descriptor] describing how
@@ -18,8 +17,7 @@ import (
 func NewDescriptorCheckIn(
 	config *model.OOAPICheckInConfig,
 ) *httpapi.Descriptor[*model.OOAPICheckInConfig, *model.OOAPICheckInResult] {
-	rawRequest, err := json.Marshal(config)
-	runtimex.PanicOnError(err, "json.Marshal failed unexpectedly")
+	rawRequest := must.MarshalJSON(config)
 	return &httpapi.Descriptor[*model.OOAPICheckInConfig, *model.OOAPICheckInResult]{
 		Accept:             httpapi.ApplicationJSON,
 		AcceptEncodingGzip: true, // we want a small response
diff --git a/internal/ooapi/th.go b/internal/ooapi/th.go
index fd057b18fb..58fefe8e28 100644
--- a/internal/ooapi/th.go
+++ b/internal/ooapi/th.go
@@ -5,12 +5,11 @@ package ooapi
 //
 
 import (
-	"encoding/json"
 	"net/http"
 
 	"github.com/ooni/probe-cli/v3/internal/httpapi"
 	"github.com/ooni/probe-cli/v3/internal/model"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 // NewDescriptorTH creates a new [httpapi.Descriptor] describing how
@@ -18,8 +17,7 @@ import (
 func NewDescriptorTH(
 	creq *model.THRequest,
 ) *httpapi.Descriptor[*model.THRequest, *model.THResponse] {
-	rawRequest, err := json.Marshal(creq)
-	runtimex.PanicOnError(err, "json.Marshal failed unexpectedly")
+	rawRequest := must.MarshalJSON(creq)
 	return &httpapi.Descriptor[*model.THRequest, *model.THResponse]{
 		Accept:             httpapi.ApplicationJSON,
 		AcceptEncodingGzip: false,
diff --git a/internal/oonirun/v2.go b/internal/oonirun/v2.go
index a6d82a5c7d..cac4e6a6ca 100644
--- a/internal/oonirun/v2.go
+++ b/internal/oonirun/v2.go
@@ -17,7 +17,7 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/httpx"
 	"github.com/ooni/probe-cli/v3/internal/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/model"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 var (
@@ -151,8 +151,7 @@ func (cache *v2DescriptorCache) PullChangesWithoutSideEffects(
 func (cache *v2DescriptorCache) Update(
 	fsstore model.KeyValueStore, URL string, entry *V2Descriptor) error {
 	cache.Entries[URL] = entry
-	data, err := json.Marshal(cache)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(cache)
 	return fsstore.Set(v2DescriptorCacheKey, data)
 }
 
@@ -209,10 +208,8 @@ var ErrNeedToAcceptChanges = errors.New("oonirun: need to accept changes")
 
 // v2DescriptorDiff shows what changed between the old and the new descriptors.
 func v2DescriptorDiff(oldValue, newValue *V2Descriptor, URL string) string {
-	oldData, err := json.MarshalIndent(oldValue, "", "  ")
-	runtimex.PanicOnError(err, "json.MarshalIndent failed unexpectedly")
-	newData, err := json.MarshalIndent(newValue, "", "  ")
-	runtimex.PanicOnError(err, "json.MarshalIndent failed unexpectedly")
+	oldData := must.MarshalAndIndentJSON(oldValue, "", "  ")
+	newData := must.MarshalAndIndentJSON(newValue, "", "  ")
 	oldString, newString := string(oldData)+"\n", string(newData)+"\n"
 	oldFile := "OLD " + URL
 	newFile := "NEW " + URL
diff --git a/internal/oonirun/v2_test.go b/internal/oonirun/v2_test.go
index fffbb9e7ff..d044a7a485 100644
--- a/internal/oonirun/v2_test.go
+++ b/internal/oonirun/v2_test.go
@@ -2,7 +2,6 @@ package oonirun
 
 import (
 	"context"
-	"encoding/json"
 	"errors"
 	"net/http"
 	"net/http/httptest"
@@ -12,7 +11,7 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/model"
 	"github.com/ooni/probe-cli/v3/internal/model/mocks"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 func TestOONIRunV2LinkCommonCase(t *testing.T) {
@@ -29,8 +28,7 @@ func TestOONIRunV2LinkCommonCase(t *testing.T) {
 				TestName: "example",
 			}},
 		}
-		data, err := json.Marshal(descriptor)
-		runtimex.PanicOnError(err, "json.Marshal failed")
+		data := must.MarshalJSON(descriptor)
 		w.Write(data)
 	}))
 	defer server.Close()
@@ -68,8 +66,7 @@ func TestOONIRunV2LinkCannotUpdateCache(t *testing.T) {
 				TestName: "example",
 			}},
 		}
-		data, err := json.Marshal(descriptor)
-		runtimex.PanicOnError(err, "json.Marshal failed")
+		data := must.MarshalJSON(descriptor)
 		w.Write(data)
 	}))
 	defer server.Close()
@@ -116,8 +113,7 @@ func TestOONIRunV2LinkWithoutAcceptChanges(t *testing.T) {
 				TestName: "example",
 			}},
 		}
-		data, err := json.Marshal(descriptor)
-		runtimex.PanicOnError(err, "json.Marshal failed")
+		data := must.MarshalJSON(descriptor)
 		w.Write(data)
 	}))
 	defer server.Close()
@@ -182,8 +178,7 @@ func TestOONIRunV2LinkEmptyTestName(t *testing.T) {
 				TestName: "", // empty!
 			}},
 		}
-		data, err := json.Marshal(descriptor)
-		runtimex.PanicOnError(err, "json.Marshal failed")
+		data := must.MarshalJSON(descriptor)
 		w.Write(data)
 	}))
 	defer server.Close()
diff --git a/internal/sessionresolver/resolver.go b/internal/sessionresolver/resolver.go
index a8b96bc996..fef523f7d9 100644
--- a/internal/sessionresolver/resolver.go
+++ b/internal/sessionresolver/resolver.go
@@ -6,7 +6,6 @@ package sessionresolver
 
 import (
 	"context"
-	"encoding/json"
 	"errors"
 	"fmt"
 	"math/rand"
@@ -18,7 +17,7 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/bytecounter"
 	"github.com/ooni/probe-cli/v3/internal/model"
 	"github.com/ooni/probe-cli/v3/internal/multierror"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 // Resolver is the session resolver. Resolver will try to use
@@ -84,8 +83,7 @@ func (r *Resolver) CloseIdleConnections() {
 
 // Stats returns stats about the session resolver.
 func (r *Resolver) Stats() string {
-	data, err := json.Marshal(r.readstatedefault())
-	runtimex.PanicOnError(err, "json.Marshal should not fail here")
+	data := must.MarshalJSON(r.readstatedefault())
 	return fmt.Sprintf("sessionresolver: %s", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter01/README.md b/internal/tutorial/measurex/chapter01/README.md
index 4c04d4ab5f..a8994b3a3b 100644
--- a/internal/tutorial/measurex/chapter01/README.md
+++ b/internal/tutorial/measurex/chapter01/README.md
@@ -45,13 +45,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 func main() {
@@ -172,8 +171,7 @@ we first convert it to the "archival" format. This is the
 data format specified at [ooni/spec](https://github.com/ooni/spec/tree/master/data-formats).
 
 ```Go
-	data, err := json.Marshal(measurex.NewArchivalDNSMeasurement(m))
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(measurex.NewArchivalDNSMeasurement(m))
 	fmt.Printf("%s\n", string(data))
 ```
 
diff --git a/internal/tutorial/measurex/chapter01/main.go b/internal/tutorial/measurex/chapter01/main.go
index fc14d9bb6d..3c0ef16605 100644
--- a/internal/tutorial/measurex/chapter01/main.go
+++ b/internal/tutorial/measurex/chapter01/main.go
@@ -46,13 +46,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 func main() {
@@ -173,8 +172,7 @@ func main() {
 	// data format specified at [ooni/spec](https://github.com/ooni/spec/tree/master/data-formats).
 	//
 	// ```Go
-	data, err := json.Marshal(measurex.NewArchivalDNSMeasurement(m))
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(measurex.NewArchivalDNSMeasurement(m))
 	fmt.Printf("%s\n", string(data))
 	// ```
 	//
diff --git a/internal/tutorial/measurex/chapter02/README.md b/internal/tutorial/measurex/chapter02/README.md
index 7edc3b2cdd..68abb09df3 100644
--- a/internal/tutorial/measurex/chapter02/README.md
+++ b/internal/tutorial/measurex/chapter02/README.md
@@ -20,13 +20,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 func main() {
@@ -74,8 +73,7 @@ chapter. Like we did before, we convert the obtained measurement
 to the "archival" data format before printing.
 
 ```Go
-	data, err := json.Marshal(measurex.NewArchivalEndpointMeasurement(m))
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(measurex.NewArchivalEndpointMeasurement(m))
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter02/main.go b/internal/tutorial/measurex/chapter02/main.go
index d39336a692..dde78df92c 100644
--- a/internal/tutorial/measurex/chapter02/main.go
+++ b/internal/tutorial/measurex/chapter02/main.go
@@ -21,13 +21,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 func main() {
@@ -75,8 +74,7 @@ func main() {
 	// to the "archival" data format before printing.
 	//
 	// ```Go
-	data, err := json.Marshal(measurex.NewArchivalEndpointMeasurement(m))
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(measurex.NewArchivalEndpointMeasurement(m))
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter03/README.md b/internal/tutorial/measurex/chapter03/README.md
index 0f0b4f3023..a27fb1f6f3 100644
--- a/internal/tutorial/measurex/chapter03/README.md
+++ b/internal/tutorial/measurex/chapter03/README.md
@@ -20,13 +20,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 func main() {
@@ -57,8 +56,7 @@ Also this operation returns a measurement, which
 we print using the usual three-liner.
 
 ```Go
-	data, err := json.Marshal(measurex.NewArchivalDNSMeasurement(m))
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(measurex.NewArchivalDNSMeasurement(m))
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter03/main.go b/internal/tutorial/measurex/chapter03/main.go
index b309980100..a922cd9963 100644
--- a/internal/tutorial/measurex/chapter03/main.go
+++ b/internal/tutorial/measurex/chapter03/main.go
@@ -21,13 +21,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 func main() {
@@ -58,8 +57,7 @@ func main() {
 	// we print using the usual three-liner.
 	//
 	// ```Go
-	data, err := json.Marshal(measurex.NewArchivalDNSMeasurement(m))
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(measurex.NewArchivalDNSMeasurement(m))
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter04/README.md b/internal/tutorial/measurex/chapter04/README.md
index f4f1118421..a0e90a3f74 100644
--- a/internal/tutorial/measurex/chapter04/README.md
+++ b/internal/tutorial/measurex/chapter04/README.md
@@ -20,14 +20,13 @@ package main
 import (
 	"context"
 	"crypto/tls"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 func main() {
@@ -69,8 +68,7 @@ As usual, the method to perform a measurement returns
 the measurement itself, which we print below.
 
 ```
-	data, err := json.Marshal(measurex.NewArchivalEndpointMeasurement(m))
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(measurex.NewArchivalEndpointMeasurement(m))
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter04/main.go b/internal/tutorial/measurex/chapter04/main.go
index 28b2553672..3714d00e5f 100644
--- a/internal/tutorial/measurex/chapter04/main.go
+++ b/internal/tutorial/measurex/chapter04/main.go
@@ -21,14 +21,13 @@ package main
 import (
 	"context"
 	"crypto/tls"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 func main() {
@@ -70,8 +69,7 @@ func main() {
 	// the measurement itself, which we print below.
 	//
 	// ```
-	data, err := json.Marshal(measurex.NewArchivalEndpointMeasurement(m))
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(measurex.NewArchivalEndpointMeasurement(m))
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter05/README.md b/internal/tutorial/measurex/chapter05/README.md
index 6d4e515c53..973c50e43d 100644
--- a/internal/tutorial/measurex/chapter05/README.md
+++ b/internal/tutorial/measurex/chapter05/README.md
@@ -26,14 +26,13 @@ package main
 import (
 	"context"
 	"crypto/tls"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 func main() {
@@ -69,8 +68,7 @@ As we did in the previous chapters, here's the usual three
 lines of code for printing the resulting measurement.
 
 ```
-	data, err := json.Marshal(measurex.NewArchivalEndpointMeasurement(m))
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(measurex.NewArchivalEndpointMeasurement(m))
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter05/main.go b/internal/tutorial/measurex/chapter05/main.go
index 4d1bef6ac6..ef55d70df3 100644
--- a/internal/tutorial/measurex/chapter05/main.go
+++ b/internal/tutorial/measurex/chapter05/main.go
@@ -27,14 +27,13 @@ package main
 import (
 	"context"
 	"crypto/tls"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 func main() {
@@ -70,8 +69,7 @@ func main() {
 	// lines of code for printing the resulting measurement.
 	//
 	// ```
-	data, err := json.Marshal(measurex.NewArchivalEndpointMeasurement(m))
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(measurex.NewArchivalEndpointMeasurement(m))
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter06/README.md b/internal/tutorial/measurex/chapter06/README.md
index 3184b88646..65c48b285a 100644
--- a/internal/tutorial/measurex/chapter06/README.md
+++ b/internal/tutorial/measurex/chapter06/README.md
@@ -29,14 +29,13 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"net/url"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 ```
@@ -46,8 +45,7 @@ into the following utility function called `print`.
 
 ```Go
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter06/main.go b/internal/tutorial/measurex/chapter06/main.go
index c242d1003e..d3f0bd47f1 100644
--- a/internal/tutorial/measurex/chapter06/main.go
+++ b/internal/tutorial/measurex/chapter06/main.go
@@ -30,14 +30,13 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"net/url"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 // ```
@@ -47,8 +46,7 @@ import (
 //
 // ```Go
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter07/README.md b/internal/tutorial/measurex/chapter07/README.md
index 2adefae5dc..0606d5a0be 100644
--- a/internal/tutorial/measurex/chapter07/README.md
+++ b/internal/tutorial/measurex/chapter07/README.md
@@ -18,13 +18,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
-	"net/url"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
@@ -45,8 +44,7 @@ The rest of the program is quite similar to what we had before.
 
 ```Go
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
@@ -57,8 +55,7 @@ func main() {
 	flag.Parse()
 	ctx, cancel := context.WithTimeout(context.Background(), *timeout)
 	defer cancel()
-	parsed, err := url.Parse(*URL)
-	runtimex.PanicOnError(err, "url.Parse failed")
+	parsed := must.ParseURL(*URL)
 	mx := measurex.NewMeasurerWithDefaultSettings()
 ```
 
diff --git a/internal/tutorial/measurex/chapter07/main.go b/internal/tutorial/measurex/chapter07/main.go
index 19172481d5..11eb399cb1 100644
--- a/internal/tutorial/measurex/chapter07/main.go
+++ b/internal/tutorial/measurex/chapter07/main.go
@@ -19,13 +19,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
-	"net/url"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
@@ -46,8 +45,7 @@ type measurement struct {
 //
 // ```Go
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
@@ -58,8 +56,7 @@ func main() {
 	flag.Parse()
 	ctx, cancel := context.WithTimeout(context.Background(), *timeout)
 	defer cancel()
-	parsed, err := url.Parse(*URL)
-	runtimex.PanicOnError(err, "url.Parse failed")
+	parsed := must.ParseURL(*URL)
 	mx := measurex.NewMeasurerWithDefaultSettings()
 	// ```
 	//
diff --git a/internal/tutorial/measurex/chapter08/README.md b/internal/tutorial/measurex/chapter08/README.md
index 4a7e2364f4..bec28398ae 100644
--- a/internal/tutorial/measurex/chapter08/README.md
+++ b/internal/tutorial/measurex/chapter08/README.md
@@ -23,13 +23,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
-	"net/url"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
@@ -39,8 +38,7 @@ type measurement struct {
 }
 
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
@@ -51,8 +49,7 @@ func main() {
 	flag.Parse()
 	ctx, cancel := context.WithTimeout(context.Background(), *timeout)
 	defer cancel()
-	parsed, err := url.Parse(*URL)
-	runtimex.PanicOnError(err, "url.Parse failed")
+	parsed := must.ParseURL(*URL)
 	mx := measurex.NewMeasurerWithDefaultSettings()
 	m := &measurement{}
 ```
diff --git a/internal/tutorial/measurex/chapter08/main.go b/internal/tutorial/measurex/chapter08/main.go
index 6b586ddd9e..52d9cbf1fb 100644
--- a/internal/tutorial/measurex/chapter08/main.go
+++ b/internal/tutorial/measurex/chapter08/main.go
@@ -24,13 +24,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
-	"net/url"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
@@ -40,8 +39,7 @@ type measurement struct {
 }
 
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
@@ -52,8 +50,7 @@ func main() {
 	flag.Parse()
 	ctx, cancel := context.WithTimeout(context.Background(), *timeout)
 	defer cancel()
-	parsed, err := url.Parse(*URL)
-	runtimex.PanicOnError(err, "url.Parse failed")
+	parsed := must.ParseURL(*URL)
 	mx := measurex.NewMeasurerWithDefaultSettings()
 	m := &measurement{}
 	// ```
diff --git a/internal/tutorial/measurex/chapter09/README.md b/internal/tutorial/measurex/chapter09/README.md
index 1f4a26f1bf..f05ea075ea 100644
--- a/internal/tutorial/measurex/chapter09/README.md
+++ b/internal/tutorial/measurex/chapter09/README.md
@@ -33,13 +33,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
-	"net/url"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
@@ -49,8 +48,7 @@ type measurement struct {
 }
 
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
@@ -61,8 +59,7 @@ func main() {
 	flag.Parse()
 	ctx, cancel := context.WithTimeout(context.Background(), *timeout)
 	defer cancel()
-	parsed, err := url.Parse(*URL)
-	runtimex.PanicOnError(err, "url.Parse failed")
+	parsed := must.ParseURL(*URL)
 	mx := measurex.NewMeasurerWithDefaultSettings()
 	m := &measurement{}
 	m.DNS = append(m.DNS, mx.LookupHostUDP(ctx, parsed.Hostname(), *address))
diff --git a/internal/tutorial/measurex/chapter09/main.go b/internal/tutorial/measurex/chapter09/main.go
index 94162f19c1..258e8d1ef8 100644
--- a/internal/tutorial/measurex/chapter09/main.go
+++ b/internal/tutorial/measurex/chapter09/main.go
@@ -34,13 +34,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
-	"net/url"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
@@ -50,8 +49,7 @@ type measurement struct {
 }
 
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
@@ -62,8 +60,7 @@ func main() {
 	flag.Parse()
 	ctx, cancel := context.WithTimeout(context.Background(), *timeout)
 	defer cancel()
-	parsed, err := url.Parse(*URL)
-	runtimex.PanicOnError(err, "url.Parse failed")
+	parsed := must.ParseURL(*URL)
 	mx := measurex.NewMeasurerWithDefaultSettings()
 	m := &measurement{}
 	m.DNS = append(m.DNS, mx.LookupHostUDP(ctx, parsed.Hostname(), *address))
diff --git a/internal/tutorial/measurex/chapter10/README.md b/internal/tutorial/measurex/chapter10/README.md
index a7c4f42f74..8dada58d8a 100644
--- a/internal/tutorial/measurex/chapter10/README.md
+++ b/internal/tutorial/measurex/chapter10/README.md
@@ -22,13 +22,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
-	"net/url"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
@@ -38,8 +37,7 @@ type measurement struct {
 }
 
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
@@ -49,8 +47,7 @@ func main() {
 	flag.Parse()
 	ctx, cancel := context.WithTimeout(context.Background(), *timeout)
 	defer cancel()
-	parsed, err := url.Parse(*URL)
-	runtimex.PanicOnError(err, "url.Parse failed")
+	parsed := must.ParseURL(*URL)
 	mx := measurex.NewMeasurerWithDefaultSettings()
 	m := &measurement{}
 ```
diff --git a/internal/tutorial/measurex/chapter10/main.go b/internal/tutorial/measurex/chapter10/main.go
index 7a72589ef5..77420e9680 100644
--- a/internal/tutorial/measurex/chapter10/main.go
+++ b/internal/tutorial/measurex/chapter10/main.go
@@ -23,13 +23,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
-	"net/url"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
@@ -39,8 +38,7 @@ type measurement struct {
 }
 
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
@@ -50,8 +48,7 @@ func main() {
 	flag.Parse()
 	ctx, cancel := context.WithTimeout(context.Background(), *timeout)
 	defer cancel()
-	parsed, err := url.Parse(*URL)
-	runtimex.PanicOnError(err, "url.Parse failed")
+	parsed := must.ParseURL(*URL)
 	mx := measurex.NewMeasurerWithDefaultSettings()
 	m := &measurement{}
 	// ```
diff --git a/internal/tutorial/measurex/chapter11/README.md b/internal/tutorial/measurex/chapter11/README.md
index 0c0fec526c..61202afe8f 100644
--- a/internal/tutorial/measurex/chapter11/README.md
+++ b/internal/tutorial/measurex/chapter11/README.md
@@ -25,18 +25,17 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter11/main.go b/internal/tutorial/measurex/chapter11/main.go
index 9df5a8edc1..2c96e925bc 100644
--- a/internal/tutorial/measurex/chapter11/main.go
+++ b/internal/tutorial/measurex/chapter11/main.go
@@ -26,18 +26,17 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter12/README.md b/internal/tutorial/measurex/chapter12/README.md
index 07d4debec8..f90d87e79c 100644
--- a/internal/tutorial/measurex/chapter12/README.md
+++ b/internal/tutorial/measurex/chapter12/README.md
@@ -22,13 +22,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 type measurement struct {
@@ -36,8 +35,7 @@ type measurement struct {
 }
 
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter12/main.go b/internal/tutorial/measurex/chapter12/main.go
index 8c4a06407b..b8bffe65db 100644
--- a/internal/tutorial/measurex/chapter12/main.go
+++ b/internal/tutorial/measurex/chapter12/main.go
@@ -23,13 +23,12 @@ package main
 
 import (
 	"context"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 type measurement struct {
@@ -37,8 +36,7 @@ type measurement struct {
 }
 
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter14/README.md b/internal/tutorial/measurex/chapter14/README.md
index 620e59c737..9c5f2000c4 100644
--- a/internal/tutorial/measurex/chapter14/README.md
+++ b/internal/tutorial/measurex/chapter14/README.md
@@ -17,7 +17,6 @@ package main
 import (
 	"context"
 	"crypto/tls"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"net/http"
@@ -25,13 +24,13 @@ import (
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/internal/tutorial/measurex/chapter14/main.go b/internal/tutorial/measurex/chapter14/main.go
index 1447bae4c1..89d9f5765d 100644
--- a/internal/tutorial/measurex/chapter14/main.go
+++ b/internal/tutorial/measurex/chapter14/main.go
@@ -18,7 +18,6 @@ package main
 import (
 	"context"
 	"crypto/tls"
-	"encoding/json"
 	"flag"
 	"fmt"
 	"net/http"
@@ -26,13 +25,13 @@ import (
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/measurex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 func print(v interface{}) {
-	data, err := json.Marshal(v)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(v)
 	fmt.Printf("%s\n", string(data))
 }
 
diff --git a/pkg/oonimkall/session.go b/pkg/oonimkall/session.go
index 5ec01dc34d..5946510a12 100644
--- a/pkg/oonimkall/session.go
+++ b/pkg/oonimkall/session.go
@@ -13,8 +13,8 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/legacy/assetsdir"
 	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/must"
 	"github.com/ooni/probe-cli/v3/internal/probeservices"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 // AtomicInt64 allows us to export atomic.Int64 variables to
@@ -326,8 +326,7 @@ func (sess *Session) Submit(ctx *Context, measurement string) (*SubmitMeasuremen
 	if err := sess.submitter.Submit(ctx.ctx, &mm); err != nil {
 		return nil, err
 	}
-	data, err := json.Marshal(mm)
-	runtimex.PanicOnError(err, "json.Marshal should not fail here")
+	data := must.MarshalJSON(mm)
 	return &SubmitMeasurementResults{
 		UpdatedMeasurement: string(data),
 		UpdatedReportID:    mm.ReportID,
diff --git a/pkg/oonimkall/task.go b/pkg/oonimkall/task.go
index 541b6dda96..0021c41187 100644
--- a/pkg/oonimkall/task.go
+++ b/pkg/oonimkall/task.go
@@ -5,7 +5,7 @@ import (
 	"encoding/json"
 	"sync/atomic"
 
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 // Task is an asynchronous task running an experiment. It mimics the
@@ -67,8 +67,7 @@ func (t *Task) WaitForNextEvent() string {
 		t.isdone.Add(1)
 		return terminated
 	}
-	data, err := json.Marshal(evp)
-	runtimex.PanicOnError(err, "json.Marshal failed")
+	data := must.MarshalJSON(evp)
 	return string(data)
 }
 
diff --git a/pkg/oonimkall/taskrunner.go b/pkg/oonimkall/taskrunner.go
index 7ec5eb12d9..608d8b7806 100644
--- a/pkg/oonimkall/taskrunner.go
+++ b/pkg/oonimkall/taskrunner.go
@@ -2,14 +2,13 @@ package oonimkall
 
 import (
 	"context"
-	"encoding/json"
 	"fmt"
 	"net/url"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/engine"
 	"github.com/ooni/probe-cli/v3/internal/model"
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 // runnerForTask runs a specific task
@@ -304,8 +303,7 @@ func (r *runnerForTask) Run(rootCtx context.Context) {
 			continue
 		}
 		m.AddAnnotations(r.settings.Annotations)
-		data, err := json.Marshal(m)
-		runtimex.PanicOnError(err, "measurement.MarshalJSON failed")
+		data := must.MarshalJSON(m)
 		r.emitter.Emit(eventTypeMeasurement, eventMeasurementGeneric{
 			Idx:     int64(idx),
 			Input:   input,
diff --git a/pkg/oonimkall/webconnectivity.go b/pkg/oonimkall/webconnectivity.go
index e96df38d4c..c4235ebd04 100644
--- a/pkg/oonimkall/webconnectivity.go
+++ b/pkg/oonimkall/webconnectivity.go
@@ -2,9 +2,8 @@ package oonimkall
 
 import (
 	"context"
-	"encoding/json"
 
-	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/must"
 )
 
 // WebConnectivityConfig contains settings for WebConnectivity.
@@ -69,8 +68,7 @@ func (r *webConnectivityRunner) run(ctx context.Context, config *WebConnectivity
 	if err != nil {
 		return nil, err
 	}
-	data, err := json.Marshal(measurement)
-	runtimex.PanicOnError(err, "json.Marshal should not fail here")
+	data := must.MarshalJSON(measurement)
 	return &WebConnectivityResults{
 		KibiBytesReceived: exp.KibiBytesReceived(),
 		KibiBytesSent:     exp.KibiBytesSent(),
diff --git a/script/nocopyreadall.bash b/script/nocopyreadall.bash
index ae8fedcc0f..8dd811cde9 100755
--- a/script/nocopyreadall.bash
+++ b/script/nocopyreadall.bash
@@ -13,6 +13,12 @@ for file in $(find . -type f -name \*.go); do
 		# inside of netxlite's own test suite.
 		continue
 	fi
+	if [ "$file" = "./internal/must/must_test.go" ]; then
+		# We're allowed to use ReadAll and Copy in this file to
+		# avoid depending on netxlite, given that netxlite's test
+		# suite already depends on must.
+		continue
+	fi
 	if grep -q 'io\.ReadAll' $file; then
 		echo "in $file: do not use io.ReadAll, use netxlite.ReadAllContext" 1>&2
 		exitcode=1