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Network Errors

If you run lychee and some links fail with the following error messages:

Terminal window
Failed: Network error: error sending request for url

or

Terminal window
Network error: Forbidden

then it could be certificate-related issue. Certificates are used to verify the identity of a website and to establish a secure connection. Different operating systems and tools have different ways to handle certificates.

If lychee is unable to verify the certificate of a website, it will show a network error. This could be due to an expired certificate, an invalid certificate, or a certificate from an unknown authority.

What now?

Double-check with a different tool

Try using a different tool like curl:

Terminal window
curl https://example.com

If this works, then the issue is with lychee and not the website. In that case, please open an issue on the lychee GitHub repository.

If it doesn’t work, then the issue is with the website or your system. It might be related to the certificate or the user agent. The site might also use a bot detection such as Cloudflare Bot Management. Read on to find out more.

Use the --insecure flag

You can use the --insecure flag to ignore certificate errors:

Terminal window
lychee --insecure https://example.com

If this works, then the issue is with the certificate. If it doesn’t work, the issue might be with lychee or the website. Please follow the steps below to narrow down the issue further.

Try a different user agent

You can try using a different user agent:

Terminal window
lychee --user-agent "curl/8.4.0" https://example.com

If this works, then the website might be blocking lychee or any other user agent that it doesn’t recognize. There’s little you can do in this case, except to contact the website administrator and ask them to whitelist lychee or keep the user agent as curl, which is a popular user agent.

If you’d like to emulate your local curl user agent, you can run:

Terminal window
curl -s https://httpbin.org/user-agent

This will show you the user agent that curl uses on your system.

Cloudflare Bot Management and other bot detection

Some websites use bot detection services like Cloudflare Bot Management to prevent automated tools from accessing their content. Unfortunately, this includes lychee, even though it does not scrape the website.

To check if the website is using Cloudflare Bot Management, you can use a service like BuiltWith. Just enter the website URL and check if it uses any bot detection services like Cloudflare Bot Management or Cloudflare Challenge.

If the website uses a bot detection service, which is blocking lychee, there’s little you can do. You can try contacting the website administrator and ask them to whitelist lychee.

Update the CA certificates

To resolve certificate-related issues, you can update the CA certificates on your system. (CA stands for Certificate Authority and is an entity that issues digital certificates. It’s what your browser uses to verify the identity of a website.)

If you’re on a Debian-based system (including Ubuntu), you can update the certificates by running:

sudo apt-get install ca-certificates

For other systems, you can follow the instructions below:

Also, see this Stack Overflow discussion for additional information.

After that, try running lychee again.

If all of the above steps don’t work, it might be a known issue with lychee. To find more information about this issue, check out the following issues:

or search for similar issues on the lychee GitHub repository.

If you can’t find an issue that matches your problem, you can open a new issue on the lychee GitHub repository.