After #4 landed the precommit fails if multiple Markdown files are present, because markdown-toc doesn't support multiple input files on its CLI. This is sad because it was the point of that PR 😅
This issue has been reported by Yajo itself here pre-commit/pre-commit#1374
My current workaround is to use the pre-commit offered by DocToc (as mentioned in the pre-commit issue).
Note: This issue is more of a heads-up for others who would run into the same problem because it would need to be fixed in the markdown-toc project directly.