Yesterday I tried something similar with a website (Go backend) that was doing a complex query/filter and showing the wrong results. I just described the problem to Claude Code, told it how to run psql, and gave it an authenticated cookie to curl the backend with. In about three minutes of playing around, it fixed the problem. It only needed raw psql and curl access, no specialized tooling, to write a bunch of bash commands to poke around and compare the backend results with the test database.