How to Validate an llms.txt File Before Publishing

A broken llms.txt is worse than no llms.txt. If the file is malformed, the tools and models that do read it get a confusing or incomplete picture of your site — the opposite of what you wanted. The good news: the llms.txt format is simple, so validation is quick once you know what to check.

This is a practical, no-fluff checklist you can run before every publish.

What the format actually requires

The llms.txt format (from llmstxt.org) is intentionally minimal Markdown:

• A single H1 title naming the project — the first line of the file.
• An optional but recommended summary blockquote (> …) right after the title.
• Zero or more H2 sections (## Docs, ## API, …), each containing a list of links.
• Each link is a list item: - [Name](https://example.com/page): short description.

That’s the whole structure. Most validation problems are deviations from this shape.

The pre-publish checklist

1. Exactly one H1, and it’s first

The file should open with one # Title line. Common mistakes:

• No H1 at all (the file starts with prose or a list).
• Multiple H1s (use ## for sections instead).
• The H1 buried below other content.

2. A summary blockquote

Right after the title, include a one-line > blockquote describing what the site or project is. It gives any reader — model or human — instant context. It’s optional in the spec, but recommended in practice.

3. Sections that group your links

Use ## headings to group related links: ## Documentation, ## API Reference, ## Guides. A flat dump of links with no sections is hard to navigate. If you have more than a handful of links, group them.

4. Well-formed links

Check every link for:

• Empty URLs — [Docs]() with nothing inside the parentheses.
• Missing link text — [](https://…) with no label.
• Malformed URLs — typos, missing https://, stray characters.
• Duplicate links — the same URL appearing more than once wastes space and signals a copy-paste error.

5. Descriptions on every link

A bare - [Quickstart](https://…) is far less useful than - [Quickstart](https://…): Get set up in five minutes. The description tells a model why the link matters and when to follow it. Add one to every list-item link.

6. Keep it concise

llms.txt is an index, not an archive. If your file is very large (tens of kilobytes or more), that’s a signal you’re stuffing full content where a curated link list belongs.

7. Consider a companion llms-full.txt

If you genuinely have a lot of long-form content models might want in full, publish a separate llms-full.txt with the complete text, and keep llms.txt as the lightweight map that links to it.

A quick example of a clean file

# Acme Docs

> Acme is an API for sending transactional email. This file indexes the docs and reference.

## Getting Started

- [Quickstart](https://acme.dev/quickstart): Send your first email in five minutes
- [Authentication](https://acme.dev/auth): API keys and scopes

## API Reference

- [Messages API](https://acme.dev/api/messages): Create and send messages
- [Webhooks](https://acme.dev/api/webhooks): Delivery and bounce events

## Optional

- [Changelog](https://acme.dev/changelog): Release notes

One H1, a summary, grouped sections, described links, no duplicates. That’s the target.

Validate it automatically

Running the checklist by hand works, but it’s easy to miss a duplicate URL or a missing description in a long file. Our free llms.txt validator checks all of the above in one pass and gives you a structure score plus specific, line-aware suggestions.

You can validate in two ways:

• Paste your content directly into the validator, or
• Enter a URL — point it at your site (we’ll fetch /llms.txt automatically) or link straight to the file. This is handy for checking a file that’s already live.

Either way you’ll see exactly what to fix before — or after — you publish.

After you fix the issues

Once the validator is happy:

1. Save the file as llms.txt and upload it to your domain root (https://example.com/llms.txt).
2. Re-run the validator against the live URL to confirm it’s served as plain text and reachable.
3. Re-check it whenever you restructure your site or add major sections.

The bottom line

Validation takes a couple of minutes and saves you from shipping a file that quietly misleads the tools reading it. Run the checklist, fix the structure, and confirm with the validator before you publish.

Don’t have a file yet? Generate a clean draft from your site with the llms.txt generator, then validate it. And if you’re still deciding whether you need one at all, see When llms.txt Makes Sense.