Hi, ast-grep author here. This is a great question and I asked this in the first place before I started the hobby project.

TLDR; I designed ast-grep to be on different tracks than semgrep.

Semgrep is for security and ast-grep is for development.

First and foremost, I have always been in awe of semgrep. Semgrep's documentation, product sites and Padioleau's podcast all gave me a lot of inspiration. Using code to find code is such a cool idea that I never need to craft an intricate regex or write a lengthy AST program. sgrep and patch from https://github.com/facebookarchive/pfff/wiki/Sgrep have helped me a lot in real large codebases.

When I used semgrep as a software engineer, instead of a security researcher, I found semgrep has not touched too much on routine development works. I can use `semgrep -e PATTERN` but the Python wrapper is not too fast compared to grep. While pattern is cool, it cannot precisely match some syntax nodes. (example, selecting generator expression in Semgrep is very hard). It also does not have API to find code programmatically.

I have also a short summary for tool comparison. https://ast-grep.github.io/advanced/tool-comparison.html