llms.txt and llms-full.txt

llms.txt is a standard for exposing website content to AI developer tools. Fern automatically generates and maintains llms.txt and llms-full.txt files for your documentation site.

Automatically serve Markdown

When Fern detects an LLM bot accessing your documentation, it automatically serves Markdown instead of HTML, reducing token consumption by 90%+.

llms.txt

Contains a lightweight summary of your documentation site with each page distilled into a one-sentence description and URL. The format is structured to help AI tools parse and understand your documentation’s hierarchy and organization.

llms.txt is available at any level of your documentation hierarchy (/llms.txt, /docs/llms.txt, /v1/api-reference/llms.txt, etc.).

Examples from Eleven Labs:

• Developer documentation (Prompting directory): elevenlabs.io/docs/best-practices/prompting/llms.txt
• API Reference (Create speech endpoint): elevenlabs.io/docs/api-reference/text-to-speech/convert/llms.txt

llms-full.txt

Contains complete documentation content including the full text of all pages. For API documentation, this includes your complete API Reference with resolved OpenAPI specifications and SDK code examples for enabled languages. Each API endpoint page includes its full OpenAPI spec.

llms-full.txt is available only at the root of your documentation site.

Example from Cash App: developers.cash.app/llms-full.txt

Control visibility for AI vs humans

Use <llms-only> and <llms-ignore> tags to provide additional context for AI assistants while keeping your documentation site clean and focused.

Content for AI only

The <llms-only> tag is included in LLM endpoints (e.g., /llms.txt, /llms-full.txt) but hidden on your documentation site. Use it for:

• Technical context that’s verbose but helpful for AI, like implementation details or architecture notes
• Code-related metadata that would clutter the human UI
• Cross-references that help AI understand relationships between pages

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<llms-only>
2
  This technical context is only visible to AI assistants via LLM endpoints.
3
</llms-only>

Content for humans only

The <llms-ignore> tag is shown on your documentation site but excluded from LLM endpoints. Use it for:

• Marketing CTAs or promotional content
• Navigation hints meant only for human readers

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<llms-ignore>
2
  <Callout intent="info">
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    This callout appears on your documentation site but not in LLM endpoints.
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  </Callout>
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</llms-ignore>

Analytics and monitoring

The Fern Dashboard provides comprehensive analytics for llms.txt usage including:

• Traffic by LLM provider (Claude, ChatGPT, Cursor, etc.)
• Page-level breakdowns of bot vs. human visitors for Markdown and llms.txt files

This visibility helps you understand LLM traffic patterns and optimize your documentation for AI consumption.