Free llms.txt Checker and Validator
Enter your website address to inspect and validate your llms.txt file for syntax errors, missing headings, and broken links with no sign-up or email.
Check Your llms.txt File
To find out if your file follows the format, enter your website address in the free llms.txt checker above. At Layer3Labs, we publish an llms.txt on the sites we operate. The checker fetches the file, tests its structure against Jeremy Howard's September 2024 proposal, and marks each check Fix, Improve, or Passed with exact instructions for every error. For an evaluation of your full site that goes beyond this single file, run our free AI visibility checker to score crawler permissions, text delivery without JavaScript, schema markup, and answer formatting out of 100 points. If you have no file yet, build one with our free llms.txt generator, which starts from a preset for your site type and downloads the finished file.
When you click Check My llms.txt, our server requests /llms.txt at your domain root or the exact .txt address you enter. It checks whether an /llms-full.txt file exists alongside it and tests the HTTP status of the first 25 links listed in your document.
The llms.txt checker reports whether your file begins with the mandatory H1 title, uses clean blockquotes, organizes files under H2 sections, and points to active destinations.
Reading Your llms.txt Report
Your report opens with an overall status headline that summarizes the condition of your file. The checker displays "Your llms.txt follows the format" when every rule passes, "N problems to fix" when your document contains structural errors, or "No valid llms.txt found" if no text file is found (an error, an HTML page or an empty file). Three counters immediately follow the headline to show your counts for "N to fix", "N to improve", and "N passed".
Below the counters, the main table displays four columns: Status, Check, What we found, and How to fix. Status marks items Fix, Improve, or Passed. The llms.txt checker runs nine checks in order.
File found marks Fix if the server returns any HTTP status code other than 200, serves an HTML document instead of plain text, or returns an empty body. Served as text marks Improve if the HTTP response Content-Type header is not text/plain or text/markdown. Starts with an H1 title marks Fix if the first non-empty line of the file does not match "# Name", because the H1 is the only required part of the proposal.
Only one H1 marks Improve if the file contains duplicate top-level title headings. Blockquote summary marks Improve if the line following your primary title does not provide a blockquote starting with "> ". No headings before the first section marks Improve if an H3 through H6 heading appears between the summary and the first H2 section, though this row appears only when it fails.
H2 sections with file lists marks Improve if the document contains no H2 headings or its sections hold no link entries at all. List items use the link format marks Improve if list entries deviate from the "- [name](url)" syntax with optional descriptive notes. Links work marks Fix if any linked address returns an HTTP error code of 400 or higher, or fails to respond.
Beneath the results table, the summary bar lists the total file size in bytes, total line count, total link entries detected, whether an Optional section exists, and whether the server found an /llms-full.txt file. The checker also offers Copy Report and a share link that re-runs the check.
In a worked example run on 25 October 2026, the checker read the specification site at https://llmstxt.org/llms.txt. The server returned HTTP 200 with Content-Type text/plain, found the primary title "llms.txt", verified a single H1, and parsed the blockquote summary. It discovered one H2 section named "Docs" holding three link entries, confirmed every link matched the markdown link structure, and verified that all three links returned valid responses. The check reported eight passed tests, zero to fix and zero to improve. The file was 637 bytes across 11 lines, and /llms-full.txt was not found.
The llms.txt Format Part by Part
The llms.txt specification published by Jeremy Howard in September 2024 defines a standardized text format designed to provide language models with clean site context. A valid file may begin with an optional byte-order mark, but it must open its visible content with an H1 title that declares the project or website name. This title represents the only strictly required section in the entire proposal.
Directly following the H1 title, the file should supply a markdown blockquote starting with "> " that contains a concise summary. This summary provides language agents with the primary context needed to interpret the rest of the document. Authors can include zero or more non-heading content sections below the summary to supply extra guidance before declaring file directories.
The core resource directory consists of zero or more H2 sections that contain markdown bullet lists. Each entry in a file list must follow the markdown hyperlink structure "- [name](url)", where the bracketed text labels the file and the parentheses enclose the target URL. Authors can append a colon and descriptive notes after the closing parenthesis to explain what information the file contains.
The proposal establishes an optional convention by allowing an H2 section named "Optional". Site owners place secondary or supplemental documentation links in this section so automated readers can safely discard them when working within constrained context windows. Learn more about file conventions in our guide to llms.txt explained. A minimal valid file structure appears as follows:
# Example Project> Example Project is an open-source data library.## Docs- [Quickstart](/docs/quickstart.md): installation steps- [API reference](/docs/api.md)## Optional- [Legacy notes](/docs/legacy.md)
Common llms.txt Failures
An HTML page served in place of the text file fails the File found check. This failure comes from sites that answer every unknown URL with their normal HTML page.
The title line causes two more failures. A file with no leading "# Name" line breaks the only required rule in the proposal and gets a Fix. More than one H1 line gets an Improve from the Only one H1 check.
Plain text bullets with no markdown link fail the List items use the link format check, because each entry needs the "- [name](url)" form. A file in a subfolder covers only the URLs under that path. Publish yours at the root, /llms.txt, to cover the whole site.
How the Link Test Works
When our server processes an llms.txt file, it extracts all URLs defined in the H2 file lists and requests the first 25 destinations to confirm their status. The checker marks the Links work check as Passed only if all tested resources return successful HTTP response codes below 400. If any single URL returns an HTTP client error such as 404 Not Found, a server error such as 500, or drops the connection, the check marks Fix and lists the broken URL.
The checker tests the first 25 links only. If your file contains 50 links, the report explicitly notes that only the first 25 URLs were evaluated.
Occasionally, a link that resolves properly in your desktop browser may fail in our checker. This typically happens when the destination server blocks the request. A slow server will also trigger a failure. Open the failing URL in a browser, and if it loads, check whether that server blocks automated requests, then re-run the check.
Full Files and Markdown Page Versions
The llms.txt proposal does not define llms-full.txt in its format section, though some sites publish one alongside llms.txt. Our llms.txt checker notes whether /llms-full.txt exists at your root path as an informative check, but it does not mark an error if the file is absent.
The formal proposal does, however, explicitly suggest providing clean markdown versions of individual web pages. Jeremy Howard recommends that publishers offer lightweight text counterparts by either appending ".md" to existing URLs, such as "page.html.md", or by replacing the file extension entirely to create "page.md".
To learn how to structure your markdown documentation endpoints alongside your root directories, review our tutorial on how to get indexed by AI through llms.txt. You can also evaluate which web crawlers have access to those resources by testing your server rules in our free AI crawler checker.
Practical Value and Verification Limits
A completely valid llms.txt file does not guarantee that any artificial intelligence platform will read, honor, or cite your content. Support for llms.txt varies across AI tools.
In its official search appearance documentation, Google Search Central states explicitly that appearing in Google AI Overviews or AI Mode requires no special AI text files and no unique schema markup.
Our llms.txt checker tests format and access only. It cannot show whether any AI tool or search engine uses the file. It evaluates a single file per run, inspecting either your root /llms.txt or the exact text URL you submit. It limits link verification to the initial 25 targets and follows the formal proposal rules, while treating content-type headers as an operational recommendation. Test your file, resolve any failing link destinations, and publish your H1 title cleanly at your site root.
Frequently Asked Questions
- Yes. The llms.txt checker is completely free to use. It requires no user account, no sign-up, and no email address to audit your site.
- The only required part of an llms.txt file is an H1 heading at the start of the visible text displaying the project or site name, formatted as "# Name". All blockquote summaries, descriptive notes, and H2 file lists remain optional in the specification.
- An llms.txt file should live at the root of your domain at /llms.txt to provide site-wide coverage. You can also publish files inside specific subdirectories, where they govern only the paths located beneath that subfolder.
- Google states in its official documentation that appearing in AI Overviews or AI Mode requires no special AI text files.
- No. The llms.txt specification does not define llms-full.txt in its format section. While some sites publish one alongside llms.txt, omitting it will not invalidate your setup.
- Your server or application framework likely uses a catch-all routing configuration that returns your standard index.html page for any URL it does not recognize, including /llms.txt. Configure your server to serve the static file directly with a text/plain or text/markdown content type.
Need Help With Your AI Search Architecture?
llms.txt, robots.txt and structured data problems often sit in different parts of a site. Layer3Labs can work through the fix list with you.
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