robots.txt is not valid

The robots.txt file tells search engines which of your site's pages they can crawl. An invalid robots.txt configuration can cause two types of problems:

  • It can keep search engines from crawling public pages, causing your content to show up less often in search results.
  • It can cause search engines to crawl pages you may not want shown in search results.

How the Lighthouse robots.txt audit fails

Lighthouse flags invalid robots.txt files:

Lighthouse audit showing invalid robots.txt

Expand the robots.txt is not valid audit in your report to learn what's wrong with your robots.txt.

Common errors include:

  • No user-agent specified
  • Pattern should either be empty, start with "/" or "*"
  • Unknown directive
  • Invalid sitemap URL
  • $ should only be used at the end of the pattern

Lighthouse doesn't check that your robots.txt file is in the correct location. To function correctly, the file must be in the root of your domain or subdomain.

How to fix problems with robots.txt

Make sure robots.txt doesn't return an HTTP 5XX status code

If your server returns a server error (an HTTP status code in the 500s) for robots.txt, search engines won't know which pages should be crawled. They may stop crawling your entire site, which would prevent new content from being indexed.

To check the HTTP status code, open robots.txt in Chrome and check the request in Chrome DevTools.

Keep robots.txt smaller than 500 KiB

Search engines may stop processing robots.txt midway through if the file is larger than 500 KiB. This can confuse the search engine, leading to incorrect crawling of your site.

To keep robots.txt small, focus less on individually excluded pages and more on broader patterns. For example, if you need to block crawling of PDF files, don't disallow each individual file. Instead, disallow all URLs containing .pdf by using disallow: /*.pdf.

Fix any format errors

  • Only empty lines, comments, and directives matching the "name: value" format are allowed in robots.txt.
  • Make sure allow and disallow values are either empty or start with / or *.
  • Don't use $ in the middle of a value (for example, allow: /file$html).

Make sure there's a value for user-agent

User-agent names to tell search engine crawlers which directives to follow. You must provide a value for each instance of user-agent so search engines know whether to follow the associated set of directives.

To specify a particular search engine crawler, use a user-agent name from its published list. (For example, here's Google's list of user-agents used for crawling.)

Use * to match all otherwise unmatched crawlers.

disallow: /downloads/

No user agent is defined.

user-agent: *
disallow: /downloads/

user-agent: magicsearchbot
disallow: /uploads/

A general user agent and a magicsearchbot user agent are defined.

Make sure there are no allow or disallow directives before user-agent

User-agent names define the sections of your robots.txt file. Search engine crawlers use those sections to determine which directives to follow. Placing a directive before the first user-agent name means that no crawlers will follow it.

# start of file
disallow: /downloads/

user-agent: magicsearchbot
allow: /

No search engine crawler will read the disallow: /downloads directive.

# start of file
user-agent: *
disallow: /downloads/

All search engines are disallowed from crawling the /downloads folder.

Search engine crawlers only follow directives in the section with the most specific user-agent name. For example, if you have directives for user-agent: * and user-agent: Googlebot-Image, Googlebot Images will only follow the directives in the user-agent: Googlebot-Image section.

Provide an absolute URL for sitemap

Sitemap files are a great way to let search engines know about pages on your website. A sitemap file generally includes a list of the URLs on your website, together with information about when they were last changed.

If you choose to submit a sitemap file in robots.txt, make sure to use an absolute URL.

sitemap: /sitemap-file.xml