See the wiki for documentation: https://github.com/palantir/phishcatch/wiki
The PhishCatch extension is available in the Chrome Web Store: https://chrome.google.com/webstore/detail/phishcatch/jgegnlkclgfifjphjmijnkmicfgckmah
Read our blog post about why we built PhishCatch and the problems it is designed to solve: https://blog.palantir.com/phishcatch-detecting-password-reuse-from-the-inside-out-77aa93e3e6fb