diff --git a/package-lock.json b/package-lock.json
index 353f2b28..9ce3945d 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -68,6 +68,7 @@
         "deserialize-error": "0.0.3",
         "dompurify": "^2.5.6",
         "fast-json-patch": "^3.1.1",
+        "fast-xml-parser": "^5.2.3",
         "graphql": "^15.8.0",
         "har-validator": "^5.1.3",
         "http-encoding": "^2.0.1",
@@ -8990,6 +8991,24 @@
       "resolved": "https://registry.npmjs.org/fast-safe-stringify/-/fast-safe-stringify-2.1.1.tgz",
       "integrity": "sha512-W+KJc2dmILlPplD/H4K9l9LcAHAfPtP6BY84uVLXQ6Evcz9Lcg33Y2z1IVblT6xdY54PXYVHEv+0Wpq8Io6zkA=="
     },
+    "node_modules/fast-xml-parser": {
+      "version": "5.2.3",
+      "resolved": "https://registry.npmjs.org/fast-xml-parser/-/fast-xml-parser-5.2.3.tgz",
+      "integrity": "sha512-OdCYfRqfpuLUFonTNjvd30rCBZUneHpSQkCqfaeWQ9qrKcl6XlWeDBNVwGb+INAIxRshuN2jF+BE0L6gbBO2mw==",
+      "funding": [
+        {
+          "type": "github",
+          "url": "https://github.com/sponsors/NaturalIntelligence"
+        }
+      ],
+      "license": "MIT",
+      "dependencies": {
+        "strnum": "^2.1.0"
+      },
+      "bin": {
+        "fxparser": "src/cli/cli.js"
+      }
+    },
     "node_modules/fastest-levenshtein": {
       "version": "1.0.16",
       "resolved": "https://registry.npmjs.org/fastest-levenshtein/-/fastest-levenshtein-1.0.16.tgz",
@@ -18714,6 +18733,18 @@
         "node": ">=0.10.0"
       }
     },
+    "node_modules/strnum": {
+      "version": "2.1.1",
+      "resolved": "https://registry.npmjs.org/strnum/-/strnum-2.1.1.tgz",
+      "integrity": "sha512-7ZvoFTiCnGxBtDqJ//Cu6fWtZtc7Y3x+QOirG15wztbdngGSkht27o2pyGWrVy0b4WAy3jbKmnoK6g5VlVNUUw==",
+      "funding": [
+        {
+          "type": "github",
+          "url": "https://github.com/sponsors/NaturalIntelligence"
+        }
+      ],
+      "license": "MIT"
+    },
     "node_modules/style-loader": {
       "version": "3.3.4",
       "resolved": "https://registry.npmjs.org/style-loader/-/style-loader-3.3.4.tgz",
@@ -28606,6 +28637,14 @@
       "resolved": "https://registry.npmjs.org/fast-safe-stringify/-/fast-safe-stringify-2.1.1.tgz",
       "integrity": "sha512-W+KJc2dmILlPplD/H4K9l9LcAHAfPtP6BY84uVLXQ6Evcz9Lcg33Y2z1IVblT6xdY54PXYVHEv+0Wpq8Io6zkA=="
     },
+    "fast-xml-parser": {
+      "version": "5.2.3",
+      "resolved": "https://registry.npmjs.org/fast-xml-parser/-/fast-xml-parser-5.2.3.tgz",
+      "integrity": "sha512-OdCYfRqfpuLUFonTNjvd30rCBZUneHpSQkCqfaeWQ9qrKcl6XlWeDBNVwGb+INAIxRshuN2jF+BE0L6gbBO2mw==",
+      "requires": {
+        "strnum": "^2.1.0"
+      }
+    },
     "fastest-levenshtein": {
       "version": "1.0.16",
       "resolved": "https://registry.npmjs.org/fastest-levenshtein/-/fastest-levenshtein-1.0.16.tgz",
@@ -35934,6 +35973,11 @@
       "resolved": "https://registry.npmjs.org/strip-json-comments/-/strip-json-comments-2.0.1.tgz",
       "integrity": "sha512-4gB8na07fecVVkOI6Rs4e7T6NOTki5EmL7TUduTs6bu3EdnSycntVJ4re8kgZA+wx9IueI2Y11bfbgwtzuE0KQ=="
     },
+    "strnum": {
+      "version": "2.1.1",
+      "resolved": "https://registry.npmjs.org/strnum/-/strnum-2.1.1.tgz",
+      "integrity": "sha512-7ZvoFTiCnGxBtDqJ//Cu6fWtZtc7Y3x+QOirG15wztbdngGSkht27o2pyGWrVy0b4WAy3jbKmnoK6g5VlVNUUw=="
+    },
     "style-loader": {
       "version": "3.3.4",
       "resolved": "https://registry.npmjs.org/style-loader/-/style-loader-3.3.4.tgz",
diff --git a/package.json b/package.json
index 4bc9698a..92ee88da 100644
--- a/package.json
+++ b/package.json
@@ -93,6 +93,7 @@
     "deserialize-error": "0.0.3",
     "dompurify": "^2.5.6",
     "fast-json-patch": "^3.1.1",
+    "fast-xml-parser": "^5.2.3",
     "graphql": "^15.8.0",
     "har-validator": "^5.1.3",
     "http-encoding": "^2.0.1",
diff --git a/src/components/editor/monaco.ts b/src/components/editor/monaco.ts
index b79f4183..245345dd 100644
--- a/src/components/editor/monaco.ts
+++ b/src/components/editor/monaco.ts
@@ -6,6 +6,7 @@ import { defineMonacoThemes } from '../../styles';
 import { delay } from '../../util/promise';
 import { asError } from '../../util/error';
 import { observable, runInAction } from 'mobx';
+import { setupXMLValidation } from './xml-validation';
 
 export type {
     MonacoTypes,
@@ -74,6 +75,8 @@ async function loadMonacoEditor(retries = 5): Promise<void> {
             },
         });
 
+        setupXMLValidation(monaco);
+
         MonacoEditor = rmeModule.default;
     } catch (err) {
         console.log('Monaco load failed', asError(err).message);
diff --git a/src/components/editor/xml-validation.ts b/src/components/editor/xml-validation.ts
new file mode 100644
index 00000000..f3f4787c
--- /dev/null
+++ b/src/components/editor/xml-validation.ts
@@ -0,0 +1,52 @@
+import type * as MonacoTypes from 'monaco-editor'
+import { XMLValidator } from 'fast-xml-parser'
+
+export function setupXMLValidation(monaco: typeof MonacoTypes) {
+    const markerId = 'xml-validation'
+    const contentChangeListeners = new Map<MonacoTypes.editor.ITextModel, MonacoTypes.IDisposable>()
+
+    monaco.editor.onWillDisposeModel(model => {
+        contentChangeListeners.delete(model)
+    })
+
+    function validate(model: MonacoTypes.editor.ITextModel) {
+        const markers: MonacoTypes.editor.IMarkerData[] = []
+        const text = model.getValue()
+
+        if (text.trim()) {
+            const validationResult = XMLValidator.validate(text, {
+                allowBooleanAttributes: true,
+            })
+
+            if (validationResult !== true) {
+                markers.push({
+                    severity: monaco.MarkerSeverity.Error,
+                    startLineNumber: validationResult.err.line,
+                    startColumn: validationResult.err.col,
+                    endLineNumber: validationResult.err.line,
+                    endColumn: model.getLineContent(validationResult.err.line).length + 1,
+                    message: validationResult.err.msg,
+                })
+            }
+        }
+
+        monaco.editor.setModelMarkers(model, markerId, markers)
+    }
+
+    monaco.editor.onDidChangeModelLanguage(({ model }) => {
+        const isXml = model.getModeId() === 'xml'
+        const listener = contentChangeListeners.get(model)
+
+        if (isXml && !listener) {
+            contentChangeListeners.set(
+                model,
+                model.onDidChangeContent(() => validate(model))
+            )
+            validate(model)
+        } else if (!isXml && listener) {
+            listener.dispose()
+            contentChangeListeners.delete(model)
+            monaco.editor.setModelMarkers(model, markerId, [])
+        }
+    })
+}