Good list of free and open source link checkers here: https://www.devopsschool.com/blog/list-of-free-open-source-s...

I've been using Xenu's Link Sleuth (https://home.snafu.de/tilman/xenulink.html) forever, but I should probably try some others out and see if there's something better now. Xenu's is also a funny throwback to the old web, sort of like the Space Jam website.