Many crates don't include a website field. When you see the crate in https://alire.ada.dev/ there's no direct way to get more information to know about the crate when exploring libraries to use. But the repository is many times the only resource you need, so you can take a look at the origin field in the command line (alr show) to discover the repository URL.

I don't see a reason why a crate should not have a website referenced, even if the page is just a repository with a README, or a basic info page where the archive is downloaded (by Alire or by direct browsing). The only reason could be for a crate that includes all the information in the manifest, and it only has a store of the archive somewhere, but that is rarely the case.

I suggest extracting the repository URL from the origin field for those crates lacking a website field and stored in well-known forges. I'm open to write the script for completing the website field in the index and prepare a pull-request, but I don't know if changing other maintainers manifests is even allowed.

There are 238 manifests without a website. Sample steps to get the list from alire-index repository root:

grep -l -R 'website *=' index | sort | tee website.txt
find index -name '*.toml' | sort | tee all.txt
join -v 1 all.txt website.txt