diff --git a/pyproject.toml b/pyproject.toml
index 39b18f23104..5a0b55ee930 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -158,6 +158,7 @@ translations = [
 ]
 types = [
     "mypy==1.15.0",
+    "pyrefly",
     "pyright==1.1.400",
     { include-group = "type-stubs" },
 ]
diff --git a/pyrefly.toml b/pyrefly.toml
new file mode 100644
index 00000000000..88ccae4d84c
--- /dev/null
+++ b/pyrefly.toml
@@ -0,0 +1,27 @@
+# Configuration file for Pyrefly_.
+# n.b. Pyrefly is early in development.
+#      Sphinx's current primary/reference type-checker is mypy.
+#
+# .. _Pyrefly: https://pyrefly.org/en/docs/configuration/
+
+project_includes = [
+    "doc/conf.py",
+    "doc/development/tutorials/examples/autodoc_intenum.py",
+    "doc/development/tutorials/examples/helloworld.py",
+    "sphinx",
+    "tests",
+    "utils",
+]
+project_excludes = [
+    "**/tests/roots*",
+]
+python_version = "3.11"
+replace_imports_with_any = [
+    "imagesize",
+    "pyximport",
+    "snowballstemmer",
+]
+
+# https://pyrefly.org/en/docs/error-kinds/
+[errors]
+implicitly-defined-attribute = false  # many false positives