April 2, 2026

Per-page directives in llms.txt

You can add a directive that's automatically prepended to every page when it's served to AI agents — both individual Markdown page URLs and each page section within llms-full.txt. The directive is only visible to agents requesting Markdown; human-facing documentation is unaffected.

agents:
  page-directive: "For a complete page index, fetch https://docs.example.com/llms.txt"

Missing redirects check rule

The missing-redirects rule for fern check detects pages that were removed or moved without a redirect. It compares your current docs navigation against the previously published state and warns when a previously published URL would return a 404.

[warning] Page "products/api-def/openapi/extensions/default.mdx" was removed. The previously published URL "/learn/api-definitions/openapi/extensions/default-values" will return 404 without a redirect. Consider adding a redirect in docs.yml to preserve existing links.

Configure its severity in docs.yml:

check:
  rules:
    missing-redirects: error

Library docs generator

Generate MDX documentation pages from your Python or C++ library source code and include them in your Fern Docs site. Configure your libraries in docs.yml, run fern docs md generate, and the generated pages appear as navigation sections alongside your other documentation.