diff --git a/build/shared/heading-slug.mts b/build/shared/heading-slug.mts
new file mode 100644
index 000000000..e831162fe
--- /dev/null
+++ b/build/shared/heading-slug.mts
@@ -0,0 +1,29 @@
+/**
+ * @file The anchor a heading gets on the built site.
+ * @author The OpenINF Authors & Friends
+ * @license MIT OR Apache-2.0 OR BlueOak-1.0.0
+ * @module {type ES6Module} build/shared/heading-slug
+ */
+
+// cspell:ignore fetchcontent
+
+/**
+ * Turns a heading's text into its anchor the way GitHub does: lowercased,
+ * punctuation other than `-` and `_` dropped, and each space a `-`.
+ *
+ * The links that point at a heading are written to that rule, by people used
+ * to GitHub and by TypeDoc, whose reference links to `logLevel?` as
+ * `#loglevel` and to `fetchContent()` as `#fetchcontent`. markdown-it-anchor
+ * keeps the punctuation instead and percent-encodes it, so those headings were
+ * `#loglevel%3F` and `#fetchcontent()`, and the links reached the top of the
+ * page rather than the heading.
+ * @param {string} text The heading's text content.
+ * @returns {string} The anchor, without the `#`.
+ */
+export function headingSlug(text: string): string {
+  return text
+    .trim()
+    .toLowerCase()
+    .replace(/[^\p{L}\p{M}\p{N}\p{Pc}\- ]/gu, '')
+    .replace(/ /g, '-');
+}
diff --git a/build/shared/heading-slug.test.mts b/build/shared/heading-slug.test.mts
new file mode 100644
index 000000000..e1ef452e3
--- /dev/null
+++ b/build/shared/heading-slug.test.mts
@@ -0,0 +1,42 @@
+/**
+ * @file Tests for the heading anchor rule.
+ * @author The OpenINF Authors & Friends
+ * @license MIT OR Apache-2.0 OR BlueOak-1.0.0
+ * @module {type ES6Module} build/shared/heading-slug.test
+ */
+
+// cspell:ignore fetchcontent
+
+import { strictEqual } from 'node:assert/strict';
+import { describe, test } from 'node:test';
+import { headingSlug } from '@openinf/portal/build/heading-slug';
+
+describe('headingSlug', () => {
+  test('matches the anchors TypeDoc links to', () => {
+    strictEqual(headingSlug('logLevel?'), 'loglevel');
+    strictEqual(headingSlug('fetchContent()'), 'fetchcontent');
+    strictEqual(headingSlug('set()?'), 'set');
+    strictEqual(headingSlug('submodule_git_url?'), 'submodule_git_url');
+  });
+
+  test('drops punctuation as GitHub does, keeping hyphens', () => {
+    strictEqual(
+      headingSlug('Show the command, not the ceremony'),
+      'show-the-command-not-the-ceremony'
+    );
+    strictEqual(
+      headingSlug('Required items (commands, arguments, etc.)'),
+      'required-items-commands-arguments-etc'
+    );
+    strictEqual(headingSlug('Questions or thoughts?'), 'questions-or-thoughts');
+    strictEqual(headingSlug('Before-and-after'), 'before-and-after');
+  });
+
+  test('keeps letters and digits from any script', () => {
+    strictEqual(headingSlug('Café naïve 2026'), 'café-naïve-2026');
+  });
+
+  test('turns every space into a hyphen', () => {
+    strictEqual(headingSlug('  a  b '), 'a--b');
+  });
+});
diff --git a/eleventy.config.mjs b/eleventy.config.mjs
index 2fb266bff..57da3b621 100644
--- a/eleventy.config.mjs
+++ b/eleventy.config.mjs
@@ -3,6 +3,7 @@ import { readdir, readFile, unlink, writeFile } from 'node:fs/promises';
 import { extname, join, parse as pathParse } from 'node:path';
 import { EleventyI18nPlugin } from '@11ty/eleventy';
 import { PATHS } from '@openinf/portal/build/constants';
+import { headingSlug } from '@openinf/portal/build/heading-slug';
 import { hasViewBox, replaceInlineSvg } from '@openinf/portal/build/inline-svg';
 import { sanitizeSdkHtml } from '@openinf/portal/build/sdk-docs';
 import autoprefixer from 'autoprefixer';
@@ -76,7 +77,7 @@ export default async function (eleventyConfig) {
 
   eleventyConfig.amendLibrary('md', (md) => {
     md.set({ highlight });
-    md.use(markdownItAnchor);
+    md.use(markdownItAnchor, { slugify: headingSlug });
     md.use(markdownItFootnote);
     // `> [!NOTE]` and the rest become a titled callout rather than a
     // blockquote opening on the literal marker. The icons it ships with come
diff --git a/package.json b/package.json
index 378da8f47..1dbaff8db 100644
--- a/package.json
+++ b/package.json
@@ -11,6 +11,7 @@
   "exports": {
     "./build/commit-message": "./build/shared/commit-message.mts",
     "./build/constants": "./build/shared/constants.mts",
+    "./build/heading-slug": "./build/shared/heading-slug.mts",
     "./build/inline-svg": "./build/shared/inline-svg.mts",
     "./build/landing": "./build/shared/landing.mts",
     "./build/pull-request": "./build/shared/pull-request.mts",