diff --git a/lib/helpers/guides.js b/lib/helpers/guides.js
index 312e67a13..04060c9f1 100644
--- a/lib/helpers/guides.js
+++ b/lib/helpers/guides.js
@@ -8,6 +8,11 @@
  * Guides are merged into the OpenAPI spec via `info.description`, which
  * Redoc renders as a top-level "Introduction" section in the sidebar and
  * splits on markdown H1/H2 headings.
+ *
+ * When `mergeGuidesIntoSpec` is called with a `{ sections }` option, guides
+ * are grouped under H1 section dividers (with each guide rendered as H2).
+ * Redoc auto-nests H2 entries under their parent H1 in the sidebar, giving
+ * the 5-section IA structure instead of a flat list.
  */
 import fs from 'fs';
 import path from 'path';
@@ -83,25 +88,75 @@ const loadGuides = (filePaths) => {
     });
 };
 
+/**
+ * Extract the leading numeric prefix from a guide file path.
+ * E.g. `/foo/07-scheduling.md` → 7, `/foo/14-cli.md` → 14.
+ * Returns null when the basename has no numeric prefix.
+ * @param {string} filePath - Absolute or relative path to the guide file.
+ * @returns {number|null} Numeric prefix, or null if not present.
+ */
+const prefixFromPath = (filePath) => {
+  const base = path.basename(String(filePath), path.extname(String(filePath)));
+  const m = base.match(/^(\d+)[-_]/);
+  return m ? parseInt(m[1], 10) : null;
+};
+
 /**
  * Merge loaded guides into an OpenAPI spec's `info.description`.
- * Each guide becomes a top-level H1 section, which Redoc renders as a
- * sidebar entry alongside the API reference.
+ *
+ * **Flat mode (default)** — each guide becomes a top-level H1 section.
+ * Redoc renders each H1 as a sidebar entry.
+ *
+ * **Sectioned mode** — when `options.sections` is provided, guides are
+ * grouped under H1 dividers (one per section) with each guide rendered as
+ * H2. Redoc auto-nests H2 entries under their parent H1 in the sidebar,
+ * giving a compact 5-section IA instead of a flat list of 18 guides.
+ * Guides whose filename prefix does not fall in any section range are
+ * appended at the end as H2 (never silently dropped).
  *
  * The original spec is mutated (and returned) to match the merge style used
  * by `initSwagger` in `lib/services/express.js`.
  *
  * @param {object} spec - OpenAPI spec object (will be mutated).
- * @param {{ title: string, body: string }[]} guides - Loaded guide entries.
- * @returns {object} The same spec, with guides appended to `info.description`.
+ * @param {{ title: string, body: string, path?: string }[]} guides - Loaded guide entries.
+ *   `path` is only required when using sectioned mode (needed for prefix extraction).
+ * @param {{ sections?: { title: string, prefixMin: number, prefixMax: number }[] } | null} [options]
+ * @returns {object|*} The mutated spec (or the original value when `spec` is falsy / not an object).
  */
-const mergeGuidesIntoSpec = (spec, guides) => {
+const mergeGuidesIntoSpec = (spec, guides, options = {}) => {
   if (!spec || typeof spec !== 'object') return spec;
   if (!Array.isArray(guides) || guides.length === 0) return spec;
 
-  const sections = guides.map(({ title, body }) => `# ${title}\n\n${body}`);
+  const { sections } = (options != null ? options : {});
+  let sectionsBlock;
+
+  if (Array.isArray(sections) && sections.length > 0) {
+    // Sectioned mode: group by filename numeric prefix
+    const groups = sections.map((sec) => ({ ...sec, guides: [] }));
+    const orphans = [];
+    for (const guide of guides) {
+      const prefix = prefixFromPath(guide.path);
+      const group = prefix !== null
+        ? groups.find((g) => prefix >= g.prefixMin && prefix <= g.prefixMax)
+        : null;
+      if (group) group.guides.push(guide);
+      else orphans.push(guide);
+    }
+    const sectionMarkdown = groups
+      .filter((g) => g.guides.length > 0)
+      .map((g) => {
+        const guideBlocks = g.guides.map(({ title, body }) => `## ${title}\n\n${body}`).join('\n\n');
+        return `# ${g.title}\n\n${guideBlocks}`;
+      });
+    const orphanBlocks = orphans.map(({ title, body }) => `## ${title}\n\n${body}`);
+    sectionsBlock = [...sectionMarkdown, ...orphanBlocks].join('\n\n');
+  } else {
+    // Flat mode (backward-compat): one H1 per guide
+    sectionsBlock = guides.map(({ title, body }) => `# ${title}\n\n${body}`).join('\n\n');
+  }
+
   const existing = typeof spec.info?.description === 'string' ? spec.info.description.trim() : '';
-  const merged = [existing, ...sections].filter(Boolean).join('\n\n');
+  const merged = [existing, sectionsBlock].filter(Boolean).join('\n\n');
 
   spec.info = { ...(spec.info || {}), description: merged };
   return spec;
@@ -112,4 +167,5 @@ export default {
   stripLeadingH1,
   loadGuides,
   mergeGuidesIntoSpec,
+  prefixFromPath,
 };
diff --git a/lib/helpers/tests/guides.sections.unit.tests.js b/lib/helpers/tests/guides.sections.unit.tests.js
new file mode 100644
index 000000000..6c1621f58
--- /dev/null
+++ b/lib/helpers/tests/guides.sections.unit.tests.js
@@ -0,0 +1,152 @@
+/**
+ * Unit tests for mergeGuidesIntoSpec — sections option — and prefixFromPath.
+ *
+ * Covers flat (backward-compat) mode and sectioned mode where guides
+ * are grouped under H1 dividers (each guide rendered as H2) using
+ * filename numeric prefix ranges. Also covers prefixFromPath edge cases
+ * (exported helper, must handle all separator / no-prefix variants).
+ */
+import GuidesHelper from '../guides.js';
+
+const { mergeGuidesIntoSpec, prefixFromPath } = GuidesHelper;
+
+describe('mergeGuidesIntoSpec — sections option:', () => {
+  const makeGuide = (filePath, body = 'guide body') => ({
+    title: filePath.replace(/.*\//, '').replace(/\.md$/, '').replace(/^\d+[-_]/, '').replace(/[-_]/g, ' '),
+    body,
+    path: filePath,
+  });
+
+  const loginGuide = makeGuide('/docs/01-login.md', 'Login content');
+  const signupGuide = makeGuide('/docs/02-signup.md', 'Signup content');
+  const subscribeGuide = makeGuide('/docs/10-subscribe.md', 'Subscribe content');
+
+  const baseSpec = () => ({ info: { description: 'overview' } });
+
+  test('without sections option: guides flatten into info.description as H1 entries', () => {
+    const out = mergeGuidesIntoSpec(baseSpec(), [loginGuide, signupGuide]);
+    expect(out.info.description).toContain('login');
+    expect(out.info.description).toContain('signup');
+    // Flat mode → H1 headings, no section grouping
+    expect(out.info.description).not.toMatch(/^# auth$/m);
+    expect(out.info.description).not.toMatch(/^# billing$/m);
+    // Flat mode → each guide is a top-level H1
+    expect(out.info.description).toMatch(/^# /m);
+  });
+
+  test('without sections option: existing description is preserved', () => {
+    const out = mergeGuidesIntoSpec(baseSpec(), [loginGuide]);
+    expect(out.info.description).toContain('overview');
+  });
+
+  test('with sections array: guides nest under H1 section dividers as H2', () => {
+    const sections = [
+      { title: 'auth', prefixMin: 1, prefixMax: 9 },
+      { title: 'billing', prefixMin: 10, prefixMax: 19 },
+    ];
+    const out = mergeGuidesIntoSpec(baseSpec(), [loginGuide, signupGuide, subscribeGuide], { sections });
+    // H1 section headers present
+    expect(out.info.description).toMatch(/^# auth$/m);
+    expect(out.info.description).toMatch(/^# billing$/m);
+    // Guides appear as H2 under their section
+    expect(out.info.description).toMatch(/^## /m);
+    // login and signup under auth (prefixes 1,2 → prefixMin:1 prefixMax:9)
+    expect(out.info.description).toContain('Login content');
+    expect(out.info.description).toContain('Signup content');
+    // subscribe under billing (prefix 10 → prefixMin:10 prefixMax:19)
+    expect(out.info.description).toContain('Subscribe content');
+  });
+
+  test('with sections: auth H1 appears before billing H1', () => {
+    const sections = [
+      { title: 'auth', prefixMin: 1, prefixMax: 9 },
+      { title: 'billing', prefixMin: 10, prefixMax: 19 },
+    ];
+    const out = mergeGuidesIntoSpec(baseSpec(), [loginGuide, signupGuide, subscribeGuide], { sections });
+    const authIdx = out.info.description.indexOf('# auth');
+    const billingIdx = out.info.description.indexOf('# billing');
+    expect(authIdx).toBeLessThan(billingIdx);
+  });
+
+  test('with sections: guides without matching prefix range become orphan H2 entries (never silently dropped)', () => {
+    const sections = [{ title: 'auth', prefixMin: 1, prefixMax: 9 }];
+    // subscribeGuide has prefix 10, outside the only section range
+    const out = mergeGuidesIntoSpec(baseSpec(), [loginGuide, subscribeGuide], { sections });
+    // The orphan is still present (not dropped)
+    expect(out.info.description).toContain('Subscribe content');
+  });
+
+  test('with sections: sections with no matched guides are omitted from output', () => {
+    const sections = [
+      { title: 'auth', prefixMin: 1, prefixMax: 9 },
+      { title: 'billing', prefixMin: 10, prefixMax: 19 },
+    ];
+    // Only auth-range guides
+    const out = mergeGuidesIntoSpec(baseSpec(), [loginGuide, signupGuide], { sections });
+    expect(out.info.description).toMatch(/^# auth$/m);
+    // billing section has no guides → should NOT appear
+    expect(out.info.description).not.toMatch(/^# billing$/m);
+  });
+
+  test('returns spec unchanged when guides array is empty', () => {
+    const spec = baseSpec();
+    const out = mergeGuidesIntoSpec(spec, []);
+    expect(out.info.description).toBe('overview');
+  });
+
+  test('returns spec unchanged when spec is falsy', () => {
+    expect(mergeGuidesIntoSpec(null, [loginGuide])).toBeNull();
+    expect(mergeGuidesIntoSpec(undefined, [loginGuide])).toBeUndefined();
+  });
+
+  test('null options does not throw — falls back to flat mode', () => {
+    // Passing null explicitly as third arg must not throw (null-safe options guard)
+    const out = mergeGuidesIntoSpec(baseSpec(), [loginGuide], null);
+    expect(out.info.description).toContain('Login content');
+    expect(out.info.description).toMatch(/^# /m);
+  });
+
+  test('with sections: orphan appears after section markdown (appended at end, not before)', () => {
+    const sections = [{ title: 'auth', prefixMin: 1, prefixMax: 9 }];
+    // subscribeGuide (prefix 10) is an orphan — should appear after the auth section
+    const out = mergeGuidesIntoSpec(baseSpec(), [loginGuide, subscribeGuide], { sections });
+    const authIdx = out.info.description.indexOf('# auth');
+    const orphanIdx = out.info.description.indexOf('Subscribe content');
+    expect(authIdx).toBeGreaterThan(-1);
+    expect(orphanIdx).toBeGreaterThan(authIdx);
+  });
+});
+
+describe('prefixFromPath:', () => {
+  test('extracts numeric prefix with dash separator', () => {
+    expect(prefixFromPath('/foo/07-scheduling.md')).toBe(7);
+    expect(prefixFromPath('/foo/14-cli.md')).toBe(14);
+    expect(prefixFromPath('/foo/01-getting-started.md')).toBe(1);
+  });
+
+  test('extracts numeric prefix with underscore separator', () => {
+    expect(prefixFromPath('/foo/03_intro.md')).toBe(3);
+    expect(prefixFromPath('/foo/20_advanced.md')).toBe(20);
+  });
+
+  test('returns null when no numeric prefix present', () => {
+    expect(prefixFromPath('/foo/welcome.md')).toBeNull();
+    expect(prefixFromPath('/foo/getting-started.md')).toBeNull();
+  });
+
+  test('returns null for pure-digit basename (no separator after digits)', () => {
+    // "42.md" has no dash or underscore after digits — not a prefix pattern
+    expect(prefixFromPath('/foo/42.md')).toBeNull();
+  });
+
+  test('handles octal-looking prefix correctly (parseInt radix 10)', () => {
+    // "08-" would be invalid octal — must parse as decimal 8
+    expect(prefixFromPath('/foo/08-webhooks.md')).toBe(8);
+    expect(prefixFromPath('/foo/09-billing.md')).toBe(9);
+  });
+
+  test('handles empty-ish inputs without throwing', () => {
+    expect(prefixFromPath('')).toBeNull();
+    expect(prefixFromPath('/foo/.md')).toBeNull();
+  });
+});