Limitation in setting new rules?

I’m new here. Can you please let me know how I may set a rule to point the error in ‘When I meet him yesterday, he is happy’?

Hi, thanks for your interest in LanguageTool. Here is our documentation about how to write rules: Development Overview - LanguageTool Wiki. One could write a simple rule that matches “meet … yesterday”, but that would cause false alarms (e.g. “I was supposed to meet him yesterday”), so some trial and error will probably be needed.