diff --git a/docs/audits/docs-last-walked.json b/docs/audits/docs-last-walked.json
new file mode 100644
index 0000000000..0967ef424b
--- /dev/null
+++ b/docs/audits/docs-last-walked.json
@@ -0,0 +1 @@
+{}
diff --git a/scripts/__tests__/check-docs-last-walked.test.mjs b/scripts/__tests__/check-docs-last-walked.test.mjs
new file mode 100644
index 0000000000..fdbe39ab5f
--- /dev/null
+++ b/scripts/__tests__/check-docs-last-walked.test.mjs
@@ -0,0 +1,55 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { checkLastWalked, parseDate } from '../check-docs-last-walked.js';
+
+const RUN = '2026-10-28';
+const PAGE = 'quickstart.mdx';
+
+// Age in days of a walk date relative to RUN, built from the same clock the script uses.
+const daysBefore = (n) => new Date(Date.parse(`${RUN}T00:00:00Z`) - n * 86400000).toISOString().slice(0, 10);
+
+test('a page with no sidecar entry warns', () => {
+  const w = checkLastWalked({ pages: [PAGE], walked: {}, runDate: RUN });
+  assert.equal(w.length, 1);
+  assert.equal(w[0].page, PAGE);
+  assert.match(w[0].message, /no walk date/);
+});
+
+test('a walk 29 days before the run date is ok', () => {
+  const w = checkLastWalked({ pages: [PAGE], walked: { [PAGE]: daysBefore(29) }, runDate: RUN });
+  assert.deepEqual(w, []);
+});
+
+test('a walk exactly 30 days before the run date is still ok', () => {
+  const w = checkLastWalked({ pages: [PAGE], walked: { [PAGE]: daysBefore(30) }, runDate: RUN });
+  assert.deepEqual(w, []);
+});
+
+test('a walk 31 days before the run date warns and names the age', () => {
+  const w = checkLastWalked({ pages: [PAGE], walked: { [PAGE]: daysBefore(31) }, runDate: RUN });
+  assert.equal(w.length, 1);
+  assert.match(w[0].message, /31 days before 2026-10-28 \(limit 30\)/);
+});
+
+test('a sidecar entry that names no page warns', () => {
+  const w = checkLastWalked({ pages: [PAGE], walked: { 'gone.mdx': RUN, [PAGE]: RUN }, runDate: RUN });
+  assert.equal(w.length, 1);
+  assert.equal(w[0].page, 'gone.mdx');
+  assert.match(w[0].message, /not a docs-site page/);
+});
+
+test('a date that is not a real YYYY-MM-DD warns instead of passing silently', () => {
+  const w = checkLastWalked({ pages: [PAGE], walked: { [PAGE]: '2026-02-30' }, runDate: RUN });
+  assert.equal(w.length, 1);
+  assert.match(w[0].message, /not a real YYYY-MM-DD/);
+});
+
+test('parseDate rejects a non-date and accepts a real one', () => {
+  assert.equal(parseDate('10/28/2026'), null);
+  assert.equal(parseDate('2026-13-01'), null);
+  assert.notEqual(parseDate('2026-10-28'), null);
+});
+
+test('a bad run date throws rather than checking against NaN', () => {
+  assert.throws(() => checkLastWalked({ pages: [], walked: {}, runDate: 'today' }), /run date must be YYYY-MM-DD/);
+});
diff --git a/scripts/check-docs-last-walked.js b/scripts/check-docs-last-walked.js
new file mode 100644
index 0000000000..9b8135daa9
--- /dev/null
+++ b/scripts/check-docs-last-walked.js
@@ -0,0 +1,110 @@
+#!/usr/bin/env node
+/**
+ * Last-walked guard for the docs site (TASK-020).
+ *
+ * Every page under `docs-site/` should carry a walk date: the day someone last
+ * followed its steps against prod. The dates live in a sidecar,
+ * `docs/audits/docs-last-walked.json`, not in page frontmatter, because public
+ * pages carry no walk records (Sam, 2026-10-28). The sidecar maps a page path
+ * (relative to `docs-site/`) to a YYYY-MM-DD date and nothing else.
+ *
+ * Warn-only: this script always exits 0. CI wiring comes in a later PR, once
+ * the dates exist.
+ *
+ * Warnings:
+ *   - a page has no entry in the sidecar
+ *   - a page's walk date is more than 30 days before the run date
+ *   - a sidecar entry names no page
+ *   - a sidecar date is not a real YYYY-MM-DD
+ *
+ * Usage: node scripts/check-docs-last-walked.js [YYYY-MM-DD]
+ * The run date defaults to today. Tests pass it explicitly.
+ */
+
+const fs = require('fs');
+const path = require('path');
+
+const MAX_AGE_DAYS = 30;
+const DAY_MS = 24 * 60 * 60 * 1000;
+const DATE_RE = /^\d{4}-\d{2}-\d{2}$/;
+
+function parseDate(value) {
+  if (typeof value !== 'string' || !DATE_RE.test(value)) return null;
+  const ms = Date.parse(`${value}T00:00:00Z`);
+  if (Number.isNaN(ms) || new Date(ms).toISOString().slice(0, 10) !== value) return null;
+  return ms;
+}
+
+/**
+ * Pure check. `pages` is an array of page paths, `walked` is the parsed sidecar
+ * object, `runDate` is YYYY-MM-DD. Returns an array of warning strings.
+ */
+function checkLastWalked({ pages, walked, runDate }) {
+  const runMs = parseDate(runDate);
+  if (runMs === null) throw new Error(`run date must be YYYY-MM-DD, got "${runDate}"`);
+
+  const warnings = [];
+  const pageSet = new Set(pages);
+
+  for (const page of pages) {
+    if (!Object.prototype.hasOwnProperty.call(walked, page)) {
+      warnings.push({ page, message: `has no walk date in docs/audits/docs-last-walked.json` });
+      continue;
+    }
+    const walkedMs = parseDate(walked[page]);
+    if (walkedMs === null) {
+      warnings.push({ page, message: `walk date "${walked[page]}" is not a real YYYY-MM-DD` });
+      continue;
+    }
+    const ageDays = Math.round((runMs - walkedMs) / DAY_MS);
+    if (ageDays > MAX_AGE_DAYS) {
+      warnings.push({
+        page,
+        message: `last walked ${walked[page]}, ${ageDays} days before ${runDate} (limit ${MAX_AGE_DAYS})`,
+      });
+    }
+  }
+
+  for (const entry of Object.keys(walked)) {
+    if (!pageSet.has(entry)) {
+      warnings.push({ page: entry, message: `is in docs/audits/docs-last-walked.json but is not a docs-site page` });
+    }
+  }
+
+  return warnings;
+}
+
+function listPages(docsDir) {
+  const out = [];
+  const walk = (dir) => {
+    for (const name of fs.readdirSync(dir, { withFileTypes: true })) {
+      const full = path.join(dir, name.name);
+      if (name.isDirectory()) walk(full);
+      else if (name.name.endsWith('.mdx')) out.push(path.relative(docsDir, full).split(path.sep).join('/'));
+    }
+  };
+  walk(docsDir);
+  return out.sort();
+}
+
+function main() {
+  const repoRoot = path.resolve(__dirname, '..');
+  const docsDir = path.join(repoRoot, 'docs-site');
+  const sidecarPath = path.join(repoRoot, 'docs', 'audits', 'docs-last-walked.json');
+  const runDate = process.argv[2] || new Date().toISOString().slice(0, 10);
+
+  const walked = fs.existsSync(sidecarPath) ? JSON.parse(fs.readFileSync(sidecarPath, 'utf8')) : {};
+  const pages = listPages(docsDir);
+  const warnings = checkLastWalked({ pages, walked, runDate });
+
+  for (const w of warnings) {
+    console.warn(`::warning file=docs-site/${w.page}::${w.page} ${w.message}`);
+  }
+  console.log(
+    `${warnings.length} last-walked warning(s) across ${pages.length} docs-site page(s) at ${runDate} (warn-only, exit 0).`,
+  );
+}
+
+if (require.main === module) main();
+
+module.exports = { checkLastWalked, parseDate, MAX_AGE_DAYS };