Calldiff

calldiff

calldiff answers "who calls whom", read straight from a git tree. It is syntactic (tree-sitter, no type checking), so it is fast and needs no build, and it will miss dynamic dispatch. Treat its output as evidence that narrows attention — never as proof that nothing else is affected.

Installed globally: run calldiff, not npx calldiff.

The three modes worth using

Add --max-depth <n> when a tree runs long. --locs is cheap and almost always worth it — line numbers make the output actionable.

Do not run bare calldiff diff

It reprints whole unchanged call trees around every change. Measured on a mid-size React monorepo: 36k tokens, versus ~18k for the raw git diff — double the cost for less information. Positional path scoping (diff HEAD <path>) silently returned nothing in the same test; do not rely on it.

Scope with --file or --entry, one target at a time. When output size is uncertain, preflight it:

calldiff diff --file <path> --token-count

Where this earns its place

• Before editing a shared helper — reach from the app entrypoint tells you which callers exist and where, in seconds, instead of a Grep sweep.
• Scoping a review — drive diff --file from the changed-file list (git diff --name-only), not across the whole repo.
• Framework noise is real. In React code every useState() and useRef() counts as a call, so component trees are mostly noise. calldiff is most useful on plain modules of named functions, least useful on component trees.

Where it does not help

Dynamic dispatch, higher-order functions, DI containers, and hook indirection do not resolve. If the answer must be complete, calldiff is a starting point and not the answer. Say so when you report what it found.

Other output formats (--format json|md) and an MCP mode exist; the CLI text output is the right default for reading and for pasting into a review.