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diffctx

diffctx

Local
diffctx.comVersion Control6Updated 1w ago
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About diffctx

diffctx analyzes a Git change to show agents and reviewers what it affects beyond the diff, including callers, tests, and contracts, then selects review context within a token budget. It runs locally and deterministically, without an index or model calls.

Key features

  1. 01Trace callers and tests affected by changes
  2. 02Select review code within a token budget
  3. 03Query symbols and multiple diff ranges
  4. 04Export ranked JSON or Markdown
  5. 05Report unresolved static call relationships

Use cases

  1. 01Review the impact of a branch or commit
  2. 02Choose relevant context for code review
  3. 03Find callers of a particular symbol
  4. 04Provide change context in CI

MCP support

The MCP server and CLI use the same analysis engine, letting MCP clients query change impact and relevant code.

Configuration

Local server config is the same for every client. Copy it into your client’s MCP config file.

mcp.json · Universal config
{
  "mcpServers": {
    "nikolay-e-diffctx": {
      "command": "uvx",
      "args": [
        "diffctx"
      ]
    }
  }
}
Run commanduvx diffctx

Local servers need a runtime on your machine (e.g. Node.js 18+). Config file locations differ by client; see your client’s docs.

Packages
pypidiffctx1.20.0

Tools

1

Saved tool list · updated 6d ago

ParameterTypeRequiredDescription
modestringNo
symbolanyNo
diff_refanyNo
clipboardbooleanNo
repo_pathstringYes
max_tokensintegerNo
fragment_idsanyNo
budget_tokensintegerNo
include_raw_diffbooleanNo

Details

From the project README

diffctx — what a git change reaches, and the code to review it

CI PyPI crates.io npm MCP Registry

diffctx tells an agent or a reviewer what a change reaches outside its diff — the callers, the tests that reach them, the contracts it crosses — and selects the code needed to understand it under a token budget. Local, deterministic, no index, no model calls. Caller resolution is static and per language; where it cannot resolve, the answer says so instead of printing a zero.

Formerly published as treemapper — every command, flag, and API call works unchanged.

Install

diffctx is a command-line tool; the MCP server, the Claude Code plugin and the GitHub Action run the same engine.

CLI
uvx diffctx . --diff HEAD~1             # zero-install, run once via uv
pipx install diffctx                    # isolated CLI
pip install diffctx                     # into an active environment
cargo install diffctx                   # native binary from crates.io, no Python
npx diffctx . --diff HEAD~1             # npm wrapper over the native binary
docker run --rm -v "$PWD:/repo" ghcr.io/nikolay-e/diffctx . --diff HEAD~1

scoop bucket add diffctx https://github.com/nikolay-e/diffctx   # Windows
scoop install diffctx/diffctx

The native binary — cargo, npm, Docker, Scoop and the release archives for Linux, macOS and Windows on x64 and ARM — answers --diff and --symbol in every mode; whole-tree export, Markdown packs, diffctx graph and the MCP server need the Python package.

Any MCP client

Registered as io.github.nikolay-e/diffctx.

claude mcp add diffctx -- uvx --from 'diffctx[mcp]' diffctx-mcp
codex mcp add diffctx -- uvx --from 'diffctx[mcp]' diffctx-mcp
gemini mcp add diffctx uvx -- --from 'diffctx[mcp]' diffctx-mcp

Cursor, VS Code, Claude Desktop, Windsurf, Zed, Continue and the Python API: integrations.

Claude Code plugin

The MCP server plus /diffctx:impact and hooks that run it on each commit and push.

claude plugin marketplace add nikolay-e/diffctx
claude plugin install diffctx@diffctx
CI

The GitHub Action hands a pull request's diff context to any review step.

Usage

diffctx . --diff --mode impact          # uncommitted work: callers outside the diff, their tests, contracts
diffctx . --symbol parse_config         # the same for a name, no change needed
diffctx . --diff main...feature         # the code to review a branch, packed under the auto budget
diffctx . --diff HEAD~1 --budget 12000  # the last commit, capped at 12k o200k tokens
diffctx . --diff 24h --mode locate      # today's work as ranked JSON, no source bodies
diffctx .                               # whole-tree export, Markdown

--diff takes a git range, staged, or a duration window ending now (24h, 90min, 2w). Every flag, default and exit code: command-line reference.

diffctx demo

How it compares

Whole-repo packers export everything; code-graph servers answer queries against a maintained index. diffctx is diff-seeded: the input is a change, the output is what it touches and what explains it. Measured results, and when the other two fit better: COMPARISON.md.

More

Apache 2.0

Comments

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