You're looking at StableBuild's Deleted PyPI mirror - where we index all deleted packages from the Python package registry.

checkmate5
5.1.0.dev4

This version was deleted from PyPI around 2025-11-29. Installing fails with:
$ pip3 install checkmate5==5.1.0.dev4 ERROR: Could not find a version that satisfies the requirement checkmate5==5.1.0.dev4
View other deleted versions of checkmate5

Install through StableBuild

You can install this package from StableBuild's PyPI snapshots from before the version was deleted:
pip3 install \ -i https://YOUR_API_KEY.pypimirror.stablebuild.com/2025-11-28/ \ checkmate5==5.1.0.dev4
Sign up for StableBuild to get an API key (it's free and takes <60 seconds!)

Or, download files manually

And install manually via pip:
checkmate5-5.1.0.dev4-py3-none-any.whl (110.3KB)
checkmate5-5.1.0.dev4.tar.gz (40.8MB)