This specification is published and recommended for implementation. Backwards-compatible additions may occur in MINOR versions; breaking changes only in MAJOR versions, with deprecation notice. See specification conventions for status definitions.
llm.txt Specification
Compatibility Variant for AI-Readable Business Identity Files
This specification defines llm.txt as a compatibility variant of llms.txt. Some AI systems request the singular filename (llm.txt) instead of the plural (llms.txt). The recommended implementation is a 301 redirect from llm.txt to llms.txt, maintaining a single source of truth.
§1 Overview
What This File Does
The llm.txt file serves the same purpose as llms.txt — providing AI systems with structured business identity and context information. It exists because some AI systems request the singular filename variant.
Why Both Files Exist
The naming convention for AI discovery files has not fully standardised. Different AI systems may request either:
llms.txt(plural) — the more common conventionllm.txt(singular) — requested by some AI systems
To ensure all AI systems can access business identity information, websites SHOULD provide both files.
For complete format details, section requirements, and implementation guidance, refer to the llms.txt Specification. This document covers only the compatibility aspects.
§2 Relationship to llms.txt
Content Requirements
The llm.txt file MUST contain identical content to llms.txt. This includes:
- Identical H1 heading (business name)
- Identical blockquote summary
- Identical sections in the same order
- Identical links and descriptions
- Identical contact information
Canonical Source
| Aspect | Guidance |
|---|---|
| Authoritative file | llms.txt is the primary file |
| Content sync | Both files MUST be updated simultaneously |
| Format | Both follow the llms.txt specification exactly |
| Validation | Both files must pass llms.txt validation rules |
Implementation Approaches
Websites MAY implement compatibility using any of these approaches:
- Server redirect (recommended): Configure HTTP 301 redirect from
llm.txttollms.txt - Symbolic link: Create
llm.txtas a symlink tollms.txt - Physical duplicate: Maintain two identical files
- Dynamic generation: Generate both files from the same source
Server redirects are the preferred approach. They maintain a single source of truth, eliminate synchronisation errors, and are correctly followed by major AI crawlers including GPTBot, ClaudeBot, and Google-Extended.
For conflict resolution when both files exist, see the Interoperability Guide.
§3 Implementation
Redirect Configuration
Configure your web server to redirect requests for /llm.txt to /llms.txt using a 301 (permanent) redirect.
Apache (.htaccess)
# Redirect llm.txt to llms.txt
Redirect 301 /llm.txt /llms.txtNginx
# In server block
location = /llm.txt {
return 301 /llms.txt;
}WordPress (via plugin or functions.php)
add_action('template_redirect', function() {
if ($_SERVER['REQUEST_URI'] === '/llm.txt') {
wp_redirect('/llms.txt', 301);
exit;
}
});IIS (web.config)
<rule name="Redirect llm.txt to llms.txt">
<match url="^llm\.txt$" />
<action type="Redirect" url="/llms.txt" redirectType="Permanent" />
</rule>File Location
The canonical file location is:
https://example.com/llms.txtWith a redirect configured for:
https://example.com/llm.txt → 301 → https://example.com/llms.txtContent Type
The llms.txt file MUST be served with:
Content-Type: text/plain; charset=utf-8Verification Checklist
/llms.txtreturns HTTP 200 status/llm.txtreturns HTTP 301 redirect to/llms.txt- The redirect target URL is correct
- Content type is correctly set for the canonical file
§4 Machine-Readable Formats
This specification is available in machine-readable formats for programmatic access:
§5 Version History
Phase 6 standardisation release. Added /specifications/roadmap/ (theme-pegged forward plan with Active/Next/Future/On hold status flags), /specifications/extensions/ (rules for experimental x- prefixed files and the promotion path), and /specifications/i18n-a11y/ (multi-language publication, locale-tagged identity fields, RTL handling, accessibility of llms.html). Added the Discovery: directive to the robots-ai.txt specification (publishers MAY advertise AI Discovery Files on the same host). Added a formal media-type stance to the HTTP behaviour page (existing IANA types, no bespoke registrations). Expanded the file integrity and signing section on the security and privacy page with four candidate mechanisms, cross-cutting concerns, and interim publisher / consumer guidance. The Discovery: directive is the only normative addition to publisher behaviour; all other additions are forward-looking documentation.
Phase 5 standardisation release. Added /specifications/related-standards/ (positioning vs llmstxt.org, IETF AI Preferences, robots.txt, Schema.org, BCP 14, JSON Schema 2020-12, SemVer) and /specifications/implementations/ (public record of conformant implementations, IETF-style). Added an explicit llmstxt.org backward-compatibility statement to the llms.txt specification. Added a formal multi-domain and subdomain scoping rule to both the llms.txt and identity.json specifications (host-scoped files, cross-host identity asserted via sameAs). No normative requirements changed for existing publishers; the new scoping rules formalise behaviour the specification already implied.
Phase 4 standardisation release. Added /specifications/processing-model/ (seven-stage algorithm for conformant consumers), /specifications/consumer-guidance/ (what AI systems should do with AI Discovery Files), /specifications/test-vectors/ (canonical test suite framing), and reference-implementation framing on the AI Visibility Checker. No normative requirements changed.
Phase 3 standardisation release. Added /specifications/versioning/ (Semantic Versioning 2.0.0 commitments, deprecation timeline, lifecycle), /specifications/governance/ (proposal lifecycle, editorial process, working principles), /specifications/security-privacy/ (trust model, content-injection patterns, GDPR considerations, integrity primitives roadmap), and /specifications/http-behaviour/ (status codes, redirects, soft-404 detection, caching, rate limits). No normative requirements changed.
Phase 2 standardisation release. Added formal conformance specification (Essential / Recommended / Complete classes). Published machine-readable registry at /specifications/registry.json, spec meta-schema, and validator-output schema. Introduced versioned JSON Schema URLs (/v1/) alongside unversioned 'latest' aliases. Added optional BCP 47 language declaration field across all applicable AI Discovery Files. No normative requirements changed.
Phase 1 standardisation release. Added 'Status of This Document' block (Stable). Normalised normative requirement keywords to uppercase per RFC 2119 and RFC 8174. Added References section linking to /specifications/conventions/ and /licensing/. No normative requirements changed.
Added AI Visibility Directory registration guidance. Minor documentation update.
Version alignment with llms.txt 1.1.0. As a compatibility variant, this file inherits all requirements from the llms.txt specification including optional sections and content restrictions.
Initial publication. Documents llm.txt as a compatibility variant of llms.txt.
Conformance
This file is required for the Complete conformance class only. A publisher claiming Complete conformance MUST publish a valid version of this file at the website's root. The Essential and Recommended classes do not require this file.
See the Conformance specification for full publisher and validator conformance criteria, including identity-consistency requirements across files and the relationship between self-declaration and Directory verification.
References
- Specification Conventions — RFC 2119 + RFC 8174 requirement keywords, document statuses, anchor naming, versioning, and language conventions used across every AI Discovery File specification.
- Licensing & Trademark — CC BY 4.0 for specification text and examples, MIT for JSON Schemas, and the free-use policy on the name "AI Discovery Files".