That would be really cool - I personally haven't used any yet, but please let me know if you find one! I always check in the browser with a color contrast checker. There are also ones that let you use a color picker and check for different font sizes, which might be handy :)
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It won't notify you automatically, but Lighthouse Reports will catch contrast issues.
There's also an abundance of Chrome Extensions out there to check (maybe one of them will alert you automatically) - I like this one.
There may be a VS Code extension that can check your CSS for you?
That would be really cool - I personally haven't used any yet, but please let me know if you find one! I always check in the browser with a color contrast checker. There are also ones that let you use a color picker and check for different font sizes, which might be handy :)