Question 1

How do I validate my llms.txt file?

Accepted Answer

You can validate your llms.txt file in two ways: enter your domain URL and the tool will fetch the file from yourdomain.com/llms.txt, or paste your llms.txt content directly into the text area. The validator checks all 9 spec rules and shows detailed pass/fail results for each check.

Question 2

What are the most common llms.txt mistakes?

Accepted Answer

The most common llms.txt validation errors include: mismatched or broken URLs (internal links to non-existent pages), multiple H1 headings (the spec allows exactly one), missing blockquote summary directly after the H1, H2 sections without proper markdown link formatting, relative URLs instead of absolute https:// URLs, and files exceeding the 50KB size limit.

Question 3

What does HTTP 200 mean for llms.txt validation?

Accepted Answer

HTTP 200 is the standard success response code from a web server. When validating by URL, the tool checks that yourdomain.com/llms.txt returns a 200 status code, meaning the file is publicly accessible and reachable at the correct location. Any other status (404, 403, 500) means AI models cannot access your llms.txt file.

Question 4

What is the maximum file size for llms.txt?

Accepted Answer

The official llms.txt specification recommends a maximum file size of 50KB (50,000 bytes). This ensures AI models can quickly ingest the file without consuming excessive token budget. Files larger than 50KB may be truncated by AI crawlers or ignored entirely.

Question 5

Why must llms.txt have exactly one H1 heading?

Accepted Answer

The llms.txt specification requires exactly one H1 heading to serve as the unique title of your file. Multiple H1 headings confuse AI models about the primary identity of the resource, while zero H1 headings fail to establish the page context. The H1 should be your site or brand name as the top-level identifier.

Question 6

What is the blockquote rule in llms.txt?

Accepted Answer

The blockquote rule requires a blockquote (prefixed with > in Markdown) directly after the H1 heading. This blockquote serves as a concise summary of what your website or content is about. AI models use this summary as the primary description of your site when citing it in responses.

Check	What It Tests	Pass Condition
File Accessibility	Is llms.txt reachable at root domain?	HTTP 200 response at /llms.txt
Single H1 Rule	Does file have exactly one H1?	Exactly 1 H1 heading found
Blockquote Summary	Is there a blockquote after H1?	`>` blockquote present
H2 Sections	Are sections organized with H2?	At least 1 H2 section
No H3+ Headings	No deep heading levels	Zero H3/H4/H5/H6 tags
Absolute URLs	Are all links absolute?	All links start with https://
Markdown Links	Correct link format?	`[Title](URL)` format used
File Size	Under 50KB?	File ≤ 50,000 bytes
Bullet Format	Links in bullet lists?	`-` or `*` bullets used

Free llms.txt Validator

What It Checks

What Does a Valid llms.txt Look Like?

The Most Common Validation Errors

1. Mismatched or Broken URLs

2. Multiple H1 Headings

3. Sub-directory Placement

Frequently Asked Questions

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