Show HN: Calldiff – a CLI to see callstack diffs in all major languages

Calldiff, a new open-source CLI tool, lets developers diff call stacks across git commits in 22 programming languages, showing which callees appeared, disappeared, or moved under an entrypoint. Built for agentic code review, it supports commands like `calldiff diff`, `calldiff tree`, and `calldiff reach`, and integrates with the incur framework for agent skills and MCP server registration.

Diff call stacks across git commits — like git diff , but for who-calls-whom. Built for agentic code review : when an agent or you rewires call flow, plain line diffs bury the shape of the change. calldiff shows which callees appeared, disappeared, or moved under an entrypoint — across 22 languages . PiService.createAgentSession options - ├─ AuthStorage.create - ├─ new ModelRegistry - ├─ createCodingTools + ├─ PiService.getServices + │ ├─ SettingsManager.create + │ ├─ AuthStorage.create + │ └─ new ModelRegistry Paste this when you want a walkthrough of call-flow changes: dearest clod, walk me through the code changes you made using npx calldiff@latest npx calldiff@latest or npm install -g calldiff HEAD vs working tree calldiff diff one ref vs working tree calldiff diff main two commits / branches calldiff diff abc123 def456 calldiff diff --from main --to feature force entrypoints functionName or ClassName.method calldiff diff main feature --entry createAgentSession calldiff diff main feature -e PiService.createAgentSession -e boot limit to paths trailing positionals; leading -- also accepted calldiff diff main feature src/lib view a call tree no diff — requires --entry calldiff tree -e createAgentSession calldiff tree HEAD -e PiService.createAgentSession calldiff tree main -e boot --max-depth 8 src/lib calldiff tree -e runCheckout --locs examples/checkout find all call paths from one symbol to another — requires --entry and --to calldiff reach -e runCheckout --to sendEmail calldiff reach HEAD -e runCheckout --to sendEmail examples/checkout agent / machine-readable output via incur calldiff diff --format json calldiff --llms calldiff skills add install agent skill files calldiff mcp add register as MCP server | Invocation | From | To | |---|---|---| calldiff diff | HEAD | working tree | calldiff diff <from | <from | working tree | calldiff diff <from <to | <from | <to | - lines were present in from and gone in to . + lines are new in to . If you omit --entry , calldiff infers exported functions whose expanded call trees changed and may show several . | Invocation | Tree from | |---|---| calldiff tree -e <name | working tree | calldiff tree <ref -e <name | that commit/ref | Prints a plain ASCII call tree no +/− markers . --entry / -e is required. With --locs , each node shows a source location: the root uses the definition file:line , and children use the call site in the parent file:line or file:line-line — same idea as LSP Call Hierarchy fromRanges , not Go to Definition. | Invocation | Paths from | |---|---| calldiff reach -e <from --to <target | working tree | calldiff reach <ref -e <from --to <target | that commit/ref | Prints every call path from the entrypoint to the target including alternate if / else arms . Both --entry / -e and --to are required. functionName — free function ClassName.method — class method new ClassName — constructor / new call Component — JSX/TSX component tags <Button / ; children nest under the parent if cond / else / else if cond — conditional arms no continuing │ rail file:line — call-site or root definition location; enable with --locs default off TypeScript, TSX, JavaScript, JSX, Python, Go, Rust, Java, Ruby, C, C++, C , PHP, Kotlin, Swift, Scala, Lua, Elixir, Bash, Haskell, Zig, Solidity, OCaml. Default: colored ASCII callstack trees TTY / colorless ASCII when piped — same shape as before.structured result --format json|yaml|md|jsonl : from / to / trees or paths with nested nodes + per-entry ascii for agents and scripts.- Built on incur https://github.com/wevm/incur : skills add , mcp add , --llms , CTAs after diffs, typed flags. - Reads source from both git trees git show / working tree - Detects language by file extension, loads a tree-sitter https://tree-sitter.github.io/tree-sitter/ grammar bundled or on-demand into ~/.cache/calldiff/grammars , and parses - Builds per-function callee lists and expands them into call trees - Diffs the trees, prints a tree, or searches paths — plus structured output for agents Grammars install on first use override cache with CALLDIFF GRAMMAR CACHE . This is syntactic AST-based , not a full typechecker — dynamic calls won’t resolve. npm run dev -- diff main HEAD --entry PiService.createAgentSession npm run dev -- tree -e runCheckout -- examples/checkout npm run dev -- reach -e runCheckout --to sendEmail -- examples/checkout