The devs at SearXNG have a bot that regularly scans the public instances for changes to the source code and delists them as a public instance if it’s altered.

If you go to https://searx.space/, they show the results of the scans for each instance.

The software is free and open source. You are encouraged to inspect the code yourself to make sure no data is collected!

Here is the source code:

https://github.com/searxng/searxng