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What an llms.txt check can—and cannot—tell you
The llms.txt proposal describes a Markdown file that gives agents concise background about a website and links to further information. It may be placed at a site root or under a narrower path. A file applies to URLs beneath its path; if more than one applies, the proposal says agents should use the most specific one. The current proposal page is v2, modified August 10, 2026: The /llms.txt file.
Do not treat llms.txt as an access-control mechanism. The proposal distinguishes it from robots.txt: llms.txt supplies information on demand, while robots.txt communicates preferences about automated access. Listing a URL—or leaving it out—does not grant or deny permission to access it.
There are two useful kinds of checks:
- Proposal conformance: whether the file follows the format rules the proposal actually states.
- Deployment usefulness: whether the intended URL responds with the expected text, its links work, and discovery mechanisms point to it.
A structurally conforming file can still be unavailable or unhelpful in production. Conversely, a third-party validator may flag a preference that the proposal does not require.
#1 Best Overall
Check the file against the proposal
1. Confirm the H1
The file should contain an H1 with the name of the project or site. This is the only required section described by the proposal. In Markdown, an H1 is commonly written with one leading hash:
# Example Site
A missing site-name H1 is a substantive format issue. By contrast, an absent blockquote, preamble, or H2 section is not, by itself, a conformance failure.
2. Check the order of elements that are present
The proposal’s order is: optional byte-order mark (BOM), H1, optional blockquote summary, optional Markdown preamble without headings, then zero or more H2 sections containing file lists. Optional elements need not be added just to satisfy a validator.
Free Markdown may appear before the H2 sections, but the proposal says this preamble should not contain headings. H2 sections are the file-list sections. If the file includes these elements, check their order rather than requiring every element to exist.
3. Inspect H2 file-list entries
Each entry in an H2 file-list section should be a Markdown link in the form [name](url). Notes may follow a link after a colon. A minimal example is:
Rank #2
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## Docs
[Getting started](https://example.com/docs): Setup and first steps
The heading labels a group; the links identify the referenced material. Do not require a section named “Optional”: that label appears as a convention in the proposal’s example, not as a mandatory section.
4. Avoid turning conventions into requirements
The proposal’s structural boundary is deliberately small: the H1 is required, while the other described components are optional. A validator can adopt additional house rules, but an extra warning should not be presented as a proposal violation unless the proposal supports that interpretation. The secondary llms.txt Format, Spec Reference is useful for comparison, but the proposal remains the primary conformance reference.
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Once the Markdown itself has been checked, test the version visitors and agents can actually retrieve. Use the path where the file is intended to apply, not just a local copy or a different path on the same site.
- Request the intended URL. Open it in a browser or use an HTTP client. Confirm that the response is successful and contains the expected Markdown rather than an error page, HTML fallback, or empty response.
- Check scope. Confirm that the file is located at the root or narrower path it is meant to describe. The proposal says a file covers URLs beneath its own path and that the most specific applicable file takes precedence.
- Follow every listed destination. Check for redirects, missing pages, access barriers, or links that resolve to irrelevant content. A syntactically valid Markdown link is not necessarily a useful destination.
- Inspect discovery signals if discovery is intended. The proposal recommends a
rel="describedby"relation for the llms.txt file and arel="alternate" type="text/markdown"relation for a Markdown version of a page. These can be provided in HTML<link>elements or HTTPLink:response headers.
These are deployment-quality checks, not extra mandatory sections in the file. A file can pass the format check without discovery relations, but those recommendations can help point agents to the file and to Markdown page versions.
Rank #3
Check Markdown page alternatives
The proposal describes ways to serve Markdown versions of pages: append .md to a URL or replace its extension with .md. For URLs without filenames, it gives index.html.md or index.md as patterns. If your site uses one of these approaches, request the corresponding URL and confirm the response is the page content in Markdown.
Do not infer that every site must use these URL patterns. They are described approaches for Markdown page versions; verify the behavior your site actually intends to provide.
Use validators without mistaking their rules for the spec
The proposal does not identify an official validator. Secondary references describe validator tools and checklists, and community validators may impose stricter checks than the proposal. Treat a validator as an aid for spotting likely problems, then assess each warning against the proposal itself. The llms.txt: the spec and its grammars reference discusses community checks; it is not a replacement for the proposal’s own requirements.
A practical review can record each finding in one of three categories:
- Conformance issue: an explicit proposal rule is not met, such as the missing H1.
- Optional convention: a tool expects an optional item, such as a blockquote or a section named “Optional.” Decide whether that convention suits the site; do not label its absence nonconformance.
- Operational issue: the file cannot be retrieved at the intended URL, or a listed link or discovery signal does not work as intended.
Troubleshoot common findings
“Missing summary” or “missing Optional section”
Check whether the validator is enforcing a house style. The blockquote and H2 file-list sections are optional, and “Optional” is not a required heading. If the H1 is present and the file otherwise follows the rules for elements it uses, these warnings alone do not establish nonconformance.
Rank #4
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“Invalid entry” in a link section
Look for a link written as [name](url). In an H2 file-list section, plain prose that is not a link may not match the proposal’s entry form. If adding explanatory notes, put them after the link, optionally preceded by a colon.
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“Heading in preamble”
Free Markdown before H2 sections should not contain headings. Move that material into prose without a heading, or organize file-list material under H2 sections using Markdown links.
The URL returns the wrong content or cannot be reached
Check the exact deployed path and response. A correct local file does not establish that the production URL serves it. Confirm the intended scope, deployment status, and that a redirect or site fallback is not returning different content.
Links work syntactically but are not useful
Open each destination and assess whether it supplies the information the link label and notes suggest. Fix stale or irrelevant targets; Markdown syntax validation cannot establish content quality.
Discovery relations are absent
First decide whether discovery is a goal for the site. The proposal recommends rel="describedby" for llms.txt and rel="alternate" type="text/markdown" for Markdown page alternatives, but these are recommendations, not mandatory file sections. If used, check the HTML link element or response header and verify the referenced URL.
When generation platforms are involved
The proposal lists platforms and plugins that support generating or serving llms.txt, including Mintlify, GitBook, Yoast SEO, AIOSEO, and Wix. This is not an endorsement and does not establish that a particular feature is available in every product plan or deployment. After enabling a platform feature, inspect the actual served file and test its links using the checks above rather than assuming the generated output is conformant.
Or skip the browser setup
For a screenshot of the deployed llms.txt page or its linked documentation, ScreenshotNeo can capture a URL with one GET request. That is separate from validating Markdown syntax or link targets; it can help you inspect a rendered page without setting up a browser.
ScreenshotNeo removes cookie banners, popups, and chat widgets before a shot; bot checks, blank pages, and failed loads are never billed; its MCP server lets AI agents take screenshots; and 1,000 screenshots a month are free with no card, with paid plans starting at $5 for 3,000. Each feature is on every plan.
cURL:
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://example.com/llms.txt -o shot.webp
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Python:
import requests
r = requests.get("https://api.screenshotneo.com/v1/shot", params={"access_key": "YOUR_API_KEY", "url": "https://example.com/llms.txt"}, timeout=90)
open("shot.webp", "wb").write(r.content)
Node.js:
const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://example.com/llms.txt' });
const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);
See the ScreenshotNeo API documentation for request options. Sign up for 1,000 free screenshots a month with no card.
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