Free llms.txt Validator & Checker
Check your file for spec compliance and agent-readiness — structure, link freshness, the agent-instructions pattern, and an llms-full.txt companion. The signals that make a file genuinely useful to AI coding assistants and agents.
We will check for /llms.txt automatically if not specified.
Structure Check
Verifies H1 headers, summaries, and correct Markdown syntax.
Link Freshness
Samples your links and flags dead ones — stale links break the agents that follow them.
Agent Readiness
Beyond compliance: detects the agent-instructions (Stripe) pattern and an llms-full.txt companion.
How to validate your llms.txt
The llms.txt standard is strict about formatting so AI coding assistants and agents (like Cursor, Claude Code, and Copilot) can parse your content efficiently.
- 1File Location — Must be at the root (e.g., example.com/llms.txt).
- 2Structure — Must start with an H1 (# Title) followed immediately by a Blockquote (> Summary).
- 3Syntax — Links must use standard Markdown `[Title](URL)` format.
Common Validation Errors
Missing Blockquote Summary
AI agents use the blockquote to quickly understand your site's purpose without reading the whole file.
Incorrect Content-Type
Your server must serve the file as text/plain or text/markdown.
No H2 Sections
Grouping your links into sections (e.g., ## Documentation) helps AI categorize your resources.
llms.txt validator FAQ
What does the llms.txt validator check?
Two sets of checks, each scored on its own. Structure (spec compliance): the file is reachable and served as text, starts with an H1 title, has a blockquote summary, uses H2 sections, and contains markdown links. Agent-readiness: whether the links are still live, whether there's an agent-instructions section, and whether a companion llms-full.txt exists.
How do I check if my llms.txt is valid?
Enter your domain or the full file URL and click Check File. The validator fetches your /llms.txt, confirms it returns HTTP 200 as text, and runs the structure and agent-readiness checks. Works on any public site, no signup.
Is a validator the same as a checker or linter?
Yes. "Validator", "checker", "tester", and "linter" all name the same job: confirming your llms.txt is well-formed and useful to AI coding assistants. This tool does all of it.
Why does structure matter for AI agents?
llms.txt is a documentation file that coding assistants and agents can read to work from your clean docs instead of scraping HTML. If the summary is missing or sections aren't marked up, there's less for a tool to work with; if a link is dead, anything that follows it hits a wall.