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

> Source: <https://github.com/tanishqkancharla/calldiff>
> Published: 2026-08-10 21:47:03+00:00

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
```