Is this for checking what Claude Code just did to your repo?

It can do that, but that's a small slice of what it does. sem parses your codebase into entities (functions, classes, methods) and builds a dependency graph across files.

So instead of line level analysis the whole granularity of seeing changes and tracking thing shifts to entities. It helps in attention mapping of your agent and lets you track the changes faster.

LSPs have been doing it for quite long but using treesitters is faster even tho type awareness is not great with this approach but overall working across multiple languages with a single tool can be quite helpful.