Yes, agreed with this completely. A friend and I were working on a small standalone Markdown linter for writing purposes and this was actually our first feature! So strange that it's not in there.

@jasonsnell, I think I listen to your podcasts sometimes. :) Yes, there is a set of link-based rules in the queue I just haven't got to yet.

I usually use https://www.npmjs.com/package/markdown-link-check since when you start to link check outside of the same document, you need to have a concept of a layout and replacements

Just tried markdown-link-check with the snippets from above:

echo 'See [Docs][] for more info.

<!-- Should have a link definition below like:
[docs]: https://example.com
-->' > ref_without_def.md
docker run -v ${PWD}:/tmp:ro --rm -i ghcr.io/tcort/markdown-link-check:stable /tmp/ref_without_def.md

echo 'See [New Docs][] for more info.

<!-- None of the link definitions match the link reference above. -->
[docs]: https://example.com' > def_without_ref.md
docker run -v ${PWD}:/tmp:ro --rm -i ghcr.io/tcort/markdown-link-check:stable /tmp/def_without_ref.md

Output (0 exit code):

FILE: /tmp/ref_without_def.md
  No hyperlinks found!

  0 links checked.

FILE: /tmp/def_without_ref.md
  No hyperlinks found!

  0 links checked.

so doesn't actually seem like it catches this case, possibly because it considers having extra refs/defs to be an okay thing to do (whereas for me it's nearly always copy-pasta, or someone forgetting how the defs/refs actually work.

Right, I missread this, but it looks like a duplicate of #144

Agree, I'll probably try to add this for the next (not pending) release.

Here is the remark-lint version of this rule https://github.com/remarkjs/remark-lint/tree/main/packages/remark-lint-no-undefined-references to see if they have any edge case code that might be needed

Right, I missread this, but it looks like a duplicate of #144

Ahh, good point, failed to find that in the issue search.

Two new rules will be available in the next release of the library:

• https://github.com/DavidAnson/markdownlint/blob/next/doc/Rules.md#md052
• https://github.com/DavidAnson/markdownlint/blob/next/doc/Rules.md#md053

They will report errors for:

• Link and image references missing a label
• Link/image reference definitions that are unused
• Link/image reference definitions that are duplicated

The latter two scenarios can be automatically fixed by the library (by deleting the unneeded reference definition).

/cc @jasonsnell

thank you @DavidAnson ! My friend might have invented Markdown? ;-)

@jasonsnell Hopefully the idea of a Markdown linter does not offend him too much.

He's working on a little one of his own for person writing use, much less comprehensive than this one. I think he likes the idea! But I don't want to speak for him.

@jasonsnell Cool. If there's anything ya'll think I should be doing here to make it more compelling (other than adding more rules), please let me know.

For example: editor integration. I happen to think the VS Code integration is pretty good (because I wrote it), but maybe you have a different favorite editor.

https://marketplace.visualstudio.com/items?itemName=DavidAnson.vscode-markdownlint