FOSS gamedev and creative worlds

Is there any way to find out which mods causes lag and uses how much ram ?

Or do we have to try each mod one by one

There exists a mod profiler. Something like mod_profiler = true in minetest.conf, then after a reasonable time has passed for sampling, run /save_mod_profile

It prints to debug.txt or console.

The Lua Optimization Tips wiki article has some information regarding measuring performance.

Ohh, that is very usefull thank you..