diffctx

# diffctx — smart diff context for LLM code review

[![CI](https://github.com/nikolay-e/diffctx/actions/workflows/ci.yml/badge.svg)](https://github.com/nikolay-e/diffctx/actions/workflows/ci.yml)
[![PyPI](https://img.shields.io/pypi/v/diffctx)](https://pypi.org/project/diffctx/)
[![crates.io](https://img.shields.io/crates/v/diffctx)](https://crates.io/crates/diffctx)
[![npm](https://img.shields.io/npm/v/diffctx)](https://www.npmjs.com/package/diffctx)
[![License](https://img.shields.io/pypi/l/diffctx)](https://pypi.org/project/diffctx/)

**diffctx selects the minimum code an LLM needs to review a git diff.**
Instead of pasting whole files, it walks the dependency graph outward from the
changed lines and stops once more context stops paying for itself.

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

## How it compares

Whole-repo packers (repomix and friends) seed on the repository and export
everything; persistent code-graph servers answer structural queries against a
maintained index. diffctx is **diff-seeded**: the input is a change, the
output is the fragments needed to understand it, packed under a hard token
budget — local, deterministic, no index, no model calls. Measured results and
when the other two families fit better: [COMPARISON.md](COMPARISON.md).

## Install

```bash
uvx diffctx . --diff HEAD~1             # zero-install, run once via uv
pipx install diffctx                    # recommended: isolated CLI, no venv needed
pip install diffctx                     # or: into an active environment
pipx install 'diffctx[mcp]'             # + MCP server for AI assistants
```

Without Python:

```bash
cargo install diffctx                   # native CLI from crates.io
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
```

On Windows, via Scoop (this repository is the bucket):

```powershell
scoop bucket add diffctx https://github.com/nikolay-e/diffctx
scoop install diffctx/diffctx
```

Prebuilt binaries for linux (x86_64/aarch64), macOS (arm64) and Windows (x64)
are attached to every [release](https://github.com/nikolay-e/diffctx/releases/latest).
The native binary and Docker image cover diff mode with YAML/JSON output and
write to stdout (redirect to capture); tree mode, Markdown output, the `graph`
subcommand and the MCP server live in the Python package.

## Quick start

```bash
diffctx . --diff HEAD~1       # smart context for last commit → paste into Claude/ChatGPT
diffctx . -f md -c            # full codebase export → clipboard in Markdown
```

![diffctx demo](https://raw.githubusercontent.com/nikolay-e/diffctx/main/docs/demo/demo.gif)

*`diffctx . --diff HEAD~1` selects only the fragments an LLM needs to review the
last commit, instead of dumping every changed file in full.*

## Diff context mode

Finds the minimal set of fragments needed to understand a change — imports,
callers, type definitions, config dependencies — across 50+ file types. It
builds a code graph (imports, co-changes, type refs), propagates relevance
outward from the changed lines, and stops when relevance drops below `--tau` or
the `--budget` token cap is hit.

`--diff` takes a git range (`HEAD~1..HEAD`, `main..feature`) or a **duration
window ending now** — `24h`, `8d`, `90min`, `1h30m`, `2w` (units `s`, `m`/`min`,
`h`, `d`, `w`, composable). A window diffs the working tree against the last
commit before it, so it covers the commits made inside the window *plus* the
uncommitted and untracked work on top — `diffctx . --diff 24h` is "everything I
touched today". A ref that happens to look like a duration (a branch `24h`)
keeps its git meaning.

| Flag        | Default | Description                                                              |
|-------------|---------|--------------------------------------------------------------------------|
| `--scoring` | `ego`   | `ego` = bounded expansion around changed nodes (fast, predictable radius); `ppr` = Personalized PageRank (global, smoother decay, slower); `bm25` = lexical retrieval against the diff hunks (baseline for sparse graphs); `rrf` = reciprocal-rank fusion of `ego` and `bm25` (widest recall, no scale calibration between the two signals); `pit` = the same fusion on score percentiles |
| `--budget`  | auto    | Cap in o200k_base tokens on the whole rendered artifact (see [Token counting](docs/product/token-budget.md)): every changed file gets one witness first, relevance fills the rest, and the renderer drops context from the tail until the document fits. A budget smaller than the summary yields the summary alone. `N` = fixed cap, `-1` disables it, `0` is a strict-zero floor (no fragments; use `--full` for changed files only) |
| `--alpha`   | 0.60    | PPR continuation probability: higher = relevance travels further from the change, lower = tighter around it (`--scoring ppr` only) |
| `--tau`     | 0.05    | Relevance threshold for full fragment content; lower-scoring fragments are stubbed or dropped (lower = more context) |
| `--full`    | false   | Only the changed files, every fragment, no related-code context          |
| `--timeout` | 300     | Wall-clock deadline in seconds; on expiry the run stops cooperatively and emits a partial artifact whose `coverage` block names the limit (exit 0). 124 is the watchdog behind it, 30 s later, for a phase that could not stop |
| `--with-raw-diff` | false | Also embed git's raw unified diff ahead of the selected fragments — additive (selection unchanged), not charged to `--budget`, lock/ignored/secret-like sections omitted. Python CLI only |
| `--mode` | `pack` | `locate` emits the same ranked selection as compact `diffctx.locate.v1` JSON — path, lines, score, provenance reasons, a blast-radius `summary` and per-item impact `group` (`test`/`type`/`config`), NO source bodies. Adds a `coverage` block naming what the run could not see (`unparsed_files`, `zero_edge_files`, `ppr_truncated`, `next_up`, a heuristic `confidence`) and an `overflow` ranking of what the budget left behind — omitted entirely when there is nothing to disclose. `diffctx . --diff --mode locate` = impact of your uncommitted change. The MCP tool takes it as `mode="locate"` |

Every JSON/YAML artifact opens with `schema: diffctx.context.v1` and validates
against [`schemas/diffctx.context.v1.json`](schemas/diffctx.context.v1.json),
generated from the engine's own type; it closes with a `provenance` block
(engine version, input object ids, the effective configuration and its hash,
the selection parameters, the tokenizer) and, when a limit stopped the run
short, a `coverage` block naming it.

### `graph` subcommand

Explore the underlying dependency graph directly, without a diff:

```bash
diffctx graph .                                  # Mermaid graph of directory deps (default)
diffctx graph . --summary                        # cycles, hotspots, coupling metrics
diffctx graph . --level fragment -f json         # fragment-level graph as JSON
diffctx graph . --level file -f graphml -o g.xml # file-level graph as GraphML
```

## Usage

<!-- BEGIN USAGE -->
```bash
# full codebase export:
diffctx .                                 # Markdown to stdout + token count
diffctx . -f md -c                        # Markdown → clipboard
diffctx . -f json -o tree.json            # JSON → file
diffctx . --no-content                    # structure only, no file contents
diffctx . --max-depth 3                   # limit depth
diffctx . -i custom.ignore                # custom ignore patterns

# diff context mode (requires git repo):
diffctx . --diff                          # uncommitted changes (working tree vs HEAD)
diffctx . --diff HEAD~1                   # context for last commit
diffctx . --diff main..feature            # context for feature branch
diffctx . --diff 24h                      # everything changed in the last 24 hours
diffctx . --diff 8d                       # same over 8 days (also 90s, 10min, 1h30m, 2w)
diffctx . --diff HEAD~1 --budget 30000    # limit to ~30k tokens
diffctx . --diff HEAD~1 -c                # diff context to clipboard
diffctx . --diff HEAD~1 --with-raw-diff   # raw patch + selected context
diffctx . --diff HEAD~1 --mode locate     # ranked navigation JSON, no source
```
<!-- END USAGE -->

Every run reports token count and size on stderr — `12,847 tokens
(o200k_base), 52.3 KB`. Counts are exact only for the GPT-4o family; Claude,
Gemini and others tokenize differently, so treat `--budget` as an upper bound
and leave headroom ([details](docs/product/token-budget.md)). Unreadable files
become placeholders like `<binary file: N bytes>`.

## Python API

```python
from pathlib import Path
from diffctx import build_diff_context, map_directory, to_json, to_markdown, to_text, to_yaml

ctx = build_diff_context(
    Path("."),
    "HEAD~1..HEAD",
    budget_tokens=None,       # None = auto; 0 = no fragments; -1 = uncapped; N = cap on the whole artifact
    alpha=0.6,
    tau=0.05,
    full=False,
    scoring_mode="ego",
    timeout=300,
    with_raw_diff=False,      # True also embeds the raw unified diff (not charged to budget)
)
print(to_markdown(ctx))

tree = map_directory(
    ".",
    max_depth=None,
    no_content=False,
    max_file_bytes=None,
    ignore_file=None,
    no_default_ignores=False,
    whitelist_file=None,
)
print(to_yaml(tree))
```

## MCP server

[![MCP Registry](https://img.shields.io/badge/MCP_Registry-io.github.nikolay--e%2Fdiffctx-blue)](https://registry.modelcontextprotocol.io/v0/servers?search=io.github.nikolay-e/diffctx)
[![diffctx MCP server](https://glama.ai/mcp/servers/nikolay-e/diffctx/badges/score.svg)](https://glama.ai/mcp/servers/nikolay-e/diffctx)

diffctx includes an [MCP](https://modelcontextprotocol.io) server that lets AI
assistants (Claude Code, Cursor, Windsurf, etc.) call diff context analysis
automatically during code review. It is published in the official MCP reg