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MCP-native code retrieval for AI agents — 84-88% fewer read tokens, BM25F + semantic search, AST chunks, session dedup

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<h2 align="center">
  
  <img width="30%" alt="pluck logo" src="assets/images/pluck_logo.png"><br/>
  The MCP-native Code Retrieval Engine for AI Agents<br/>
  <sub>84-88 % fewer tokens on code reads · 71 % shorter CI logs · 0.07 ms warm search — every number gated by <a href="benchmarks/baseline.json"><code>benchmarks/baseline.json</code></a></sub>
</h2>

[Quickstart](#quickstart) •
[Why Pluck?](#why-pluck) •
[MCP Tools](#mcp-tools) •
[CLI](#standalone-cli-no-agent) •
[Benchmarks](#performance--token-savings)

</div>

**pluck** is a local Rust daemon that replaces `cat` and `grep` as the default way AI agents read and search code. It exposes symbol-aware code reading and search to agents over the Model Context Protocol (MCP). Smart outlines cut eligible code-read tokens by **84-88 %**, CI logs compress by **71 %**, and warm search stays sub-millisecond — with a `--raw` fallback on every tool so the agent never loses capability by defaulting to pluck.

```
Without pluck:  ls → grep → cat file1 → cat file2 → cat file3 → ...
With pluck:     pluck.plan "fix auth-token expiry"  → 3-5 next-call recommendations
                pluck.search "auth flow"            → ranked chunks, BM25 + semantic
                pluck.peek validate_token           → signature + callees only
                pluck.symbol validate_token         → just that function's body
                pluck.impact validate_token         → every caller, depth-capped
                pluck.deps src/auth/login.ts        → forward/reverse import graph
                pluck.digest < cargo-build.log      → 71 % shorter, errors intact
```

## Quickstart

Pluck is designed to be the default retrieval tool for your AI coding agents.

### 1. Paste the Agent Setup Prompt

```text
Install and configure pluck for this repo.

Install / register:
- If pluck is missing, install pluck-mcp and pluck-cli with Cargo or Homebrew.
- Register pluckd as an MCP server named `pluck` for this repository.
- Prefer project-scoped config when the agent supports it.
- Preserve existing MCP servers, rules, hooks, permissions, and comments.

To make pluck the first retrieval choice:
- Use the strongest official mechanism this agent supports.
- Claude Code: use project MCP config or
  `claude mcp add --transport stdio --scope project pluck -- pluckd --repo <repo-root>`;
  approve the `pluck` MCP server in settings/permissions when needed; add
  durable instructions in `CLAUDE.md`; use PreToolUse hooks or permission
  deny rules only when they can safely redirect repo-local cat/grep/rg/read
  retrieval to mcp__pluck__* tools.
- Codex: use `codex mcp add pluck -- pluckd --repo <repo-root>` or
  `~/.codex/config.toml` / trusted project `.codex/config.toml`; add the
  pluck-first retrieval policy to `AGENTS.md`.
- Cursor: use project `.cursor/mcp.json`; add an always-applied Project Rule
  in `.cursor/rules/` or an `AGENTS.md` instruction for the workspace.

Pluck-first retrieval policy:
- Use mcp__pluck__read before cat, head, tail, sed -n, or built-in file reads
  for files inside the indexed repo.
- Use mcp__pluck__search for conceptual code lookup.
- Use mcp__pluck__grep before grep or rg for exact strings, regexes, TODOs,
  and all textual matches inside the repo.
- Use mcp__pluck__peek, mcp__pluck__symbol, mcp__pluck__expand,
  mcp__pluck__impact, and mcp__pluck__deps for symbol shape, bodies, call
  chains, refactor impact, and import relationships.
- Use mcp__pluck__digest before pasting long cargo, npm, pytest, or GitHub
  Actions logs into context.
- Fall back to Bash or built-in reads only for binary files, paths outside the
  repo, byte-exact shell pipelines, unsupported formats, or when pluck is
  unavailable.

Verify:
- Restart or reload the agent if MCP changes require it.
- Confirm the `pluck` MCP server is connected and mcp__pluck__* tools exist.
- Run one repo code-search/read task and confirm the agent calls mcp__pluck__*
  before Bash, grep/rg, cat, or built-in file reads.
- Show the files changed and the verification result.
```

For an expanded version with safety checks and fallback instructions, use the
[full agent install prompt](docs/AGENT_INSTALL.md).

### 2. Or set it up manually

```bash
# Daemon + standalone CLI from crates.io
cargo install pluck-mcp pluck-cli

# Or via Homebrew tap
brew tap hunhee98/pluck && brew install pluck
```

**Claude Code**
```bash
pluck init --target claude --mode aggressive  # MCP + permissions + Bash retrieval block
```
*(Alternatively, you can manually enable it via `/plugin marketplace add hunhee98/pluck`)*

**Codex**
```bash
pluck init --target codex --mode strong  # MCP + AGENTS.md pluck-first policy
```

**Cursor**
```bash
pluck init --target cursor --mode strong  # MCP + always-apply Cursor rule
```

## Why pluck?

When AI agents use standard `cat` and `grep` to explore a codebase, they waste massive amounts of context window tokens. Re-reading the same file chunk, scrolling past unrelated functions, and re-paying tokens for identical imports on every read adds up to thousands of wasted tokens per session.

pluck solves this by providing an **agent-facing layer** for code search. Its core principle: **every retrieval call an agent makes should default to pluck.** Bash is only the fallback when pluck legitimately can't help (e.g., binary files, paths outside the repo).

- **Smart Outline (`pluck.read`)**: Instead of dumping a 1,000-line file, it returns a token-efficient outline of signatures with tiny helper bodies inline. The agent can then fetch only the larger function bodies it needs.
- **Session Dedup**: If an agent searches for "auth" and later searches for "token", any overlapping code chunks are replaced with a 1-token placeholder (`[already-shown: ...]`). The bytes are already in the agent's context; repeating them is pure waste.
- **Lossless Default**: Stripping comments or dropping types hurts the agent's decision-making. pluck keeps the original bytes intact and makes lossy modes strictly opt-in.
- **100% Capability Guarantee**: Every pluck tool has a `--raw` fallback that behaves exactly like `cat` or `grep` byte-for-byte.

## How it works

pluck chunks files at the Abstract Syntax Tree (AST) level using Tree-sitter. When an agent queries, pluck ranks these chunks using a hybrid of keyword matching (BM25F over symbol/signature/content) and semantic similarity (a static `model2vec`-style lookup, [`potion-code-16M`](https://huggingface.co/minishlab/potion-code-16M), ~60 MB on disk — no transformer inference at runtime). Search expands natural-language BM25 queries with embedding-nearest terms from the indexed repo, then runs a two-stage cascade: BM25F first widens the candidate pool, embeddings rerank that pool, and a smaller semantic-rescue pass catches concept queries with weak lexical overlap. The RRF blend is picked continuously from the query embedding against natural-language and code centroids, so agents can search by concept ("payment flow") without losing precision on exact symbols.

<p align="center">
  <img src="assets/images/architecture_overview.png" alt="Architecture Overview">
</p>

### Session dedup in action

<p align="center">
  <img src="assets/images/session_dedup_flow.png" alt="Session Dedup Flow">
</p>

## MCP Tools

Agents call specific tools depending on what they need. Bash is the fallback, not the default.

| Tool (wire name) | Replaces | Use when |
|------------------|----------|----------|
| `mcp__pluck__read` | `cat` | Read a code file (smart outline by default; `raw: true` for byte-exact) |
| `mcp__pluck__grep` | `grep` / `rg` | Keyword search (all ripgrep flags wrapped) |
| `mcp__pluck__search` | — | Ranked-chunk search (BM25 + semantic RRF) |
| `mcp__pluck__symbol` | `cat` + scroll | Read just that function/class |
| `mcp__pluck__peek` | — | Signature + direct callees only |
| `mcp__pluck__expand` | many `cat`s | Symbol + callees up to N hops |
| `mcp__pluck__impact` | grep + read each caller | Reverse call graph — "who calls this symbol?" |
| `mcp__pluck__deps` | grep imports + read each file | File-level import graph — "what does this file depend on / who imports it?" |
| `mcp__pluck__digest` | piping `cargo build`/`pytest`/CI logs to `cat` | Compress verbose tool output (errors / panics kept verbatim, progress lines collapsed) |
| `mcp__pluck__plan` | speculative `search`/`read` loop | Given a free-form task, recommend the next 3-5 retrieval calls + confidence indicator |

## Standalone CLI (no agent)

You can also use pluck directly in your terminal:

```bash
pluck index .
pluck search "auth flow" --repo .
pluck read src/auth/login.ts        # smart outline
pluck read src/auth/login.ts --raw  # byte-equivalent cat
```

## Performance & Token Savings

Every number on this page cites a frozen baseline row or a measured scenario. No projected / aspirational percentages.

<p align="center">
  <img src="assets/images/token_savings_chart.png" alt="Token Savings Chart">
</p>

### Gated engine metrics

These are the invariants in [`benchmarks/baseline.json`](benchmarks/baseline.json). Every commit that touches engine-core runs `scripts/regression-gate.py` and the gate fails the build if any of them drift past tolerance.

| Metric | Value | Source row in `baseline.json` |
|--------|-------|-------------------------------|
| Chunker p50 (medium repo, 500 lines) | **1.05 ms** | `chunker_medium_ms_p50` |
| Indexer throughput (medium, 500 files) | **2 747 files/s** | `indexer_files_per_sec_medium` |
| Warm search p50 (medium) | **0.07 ms** | `warm_search_p50_ms_medium` |
| File save → searchable p50 | **171 ms** | `freshness_p50_ms_medium` |
| Session-dedup savings (5-query bench) | **23 %** | `session_dedup_session_savings_pct` |
| `pluck.digest` log compression (median of 6 fixtures) | **71 %** | `digest_savings_pct` |

### Eligible read-token savings

`pluck.read` outline mode is where pluck stops agents from paying the `cat` tax: instead of dumping every line, it returns the file's symbol map, inlines tiny helper bodies, and lets the agent fetch larger bodies on demand.

| Read workload | `cat` tokens | `pluck.read` tokens | Savings |
|---------------|-------------:|--------------------:|--------:|
| medium realistic (5 fns, ~120 lines) | 929 | 116 | **88 %** |
| large realistic (25 fns, ~600 lines) | 4 549 | 556 | **88 %** |
| xl realistic (100 fns, ~2 400 lines) | 18 124 | 2 320 | **87 %** |
| class (1 class + 50 methods) | 8 608 | 1 302 | **85 %** |

Tiny files and `raw` reads are control cases: they are expected to show little or no savings because byte-exact fallback is the point.

### Measured single-scenario token reduction

`fix-auth-token-expiry`: same JIRA-style task, bash workflow (`rg -l` + several `cat`s) vs pluck workflow (`search` + `read` + `symbol`). Both runners arrive at the same fix:

| Runner | Tokens spent | Source |
|--------|--------------|--------|
| bash (`rg + cat`) | 1 248 | [`fix-auth-token-expiry-1778750775.json`](benchmarks/results/fix-auth-token-expiry-1778750775.json) |
| **pluck** (`search + read + symbol`) | **931 (−25 %)** | same file |

Broader LLM-in-the-loop measurements across `fix` / `refactor` / `explore` / `search` / `review` scenarios are roadmapped as v0.8.0 work. We'll publish those numbers when they exist, not before.

### Feature Comparison

| Capability | `cat` + `grep` / `rg` | Other code-search tools | **pluck** |
|------------|----------------------|-------------------------|-----------|
| Hybrid BM25 + semantic ranking | ✗ | typically ✓ | ✓ |
| AST-level chunks | ✗ | typically ✓ | ✓ |
| Persistent daemon (MCP stdio) | — | ✗ (cold CLI per call) | **✓** |
| Persistent on-disk index (mmap) | — | usually ✗ | ✗ — roadmapped (v0.7.0) |
| Incremental reindex (file watcher) | — | usually ✗ | **✓ — 171 ms p50** |
| **Session-scoped dedup** | — | ✗ | **✓ — 23 % savings on bench** |
| **`--raw` cat/grep byte parity** | — | ✗ | **✓** |
| **Lossless default, lossy opt-in** | — | varies | **✓** |
| `peek` (signature + direct callees) | ✗ | ✗ | **✓** |
| Single-file outline (`pluck.read`) | ✗ | ✗ | **✓** |
| Multi-hop `expand` (call graph) | ✗ | ✗ | **✓** |
| Reverse call graph (`impact`) | ✗ | ✗ | **✓** |
| File-level import graph (`deps`) | ✗ | ✗ | **✓** |
| Build / CI / test log compression (`digest`) | ✗ | ✗ | **✓ — 71 % median** |
| Exploration recommender (`plan`) | ✗ | ✗ | **✓** |

## Supported formats

pluck AST-chunks **20+ code and project formats** (26 today) via
Tree-sitter. Every format below is covered by a chunker unit test in
[`crates/pluck-core/src/chunker`](crates/pluck-core/src/chunker); the
list is the `Lang` enum in
[`lang.rs`](crates/pluck-core/src/chunker/lang.rs), so this section and
the code cannot drift.

| Group | Formats |
|-------|---------|
| **Languages** | Rust, TypeScript, TSX, JavaScript, Python, Go, Java, Kotlin, Swift, Ruby, PHP, C, C++ |
| **Web / component** | HTML, CSS, SCSS, Svelte |
| **Data / config** | JSON, YAML, TOML, SQL, HCL / Terraform |
| **Schema / docs / infra** | GraphQL, Markdown, MDX, Dockerfile, Shell |

Anything not in this list still works through `pluck.read --raw` /
`pluck.grep` (byte-equivalent to `cat` / `rg`); it just doesn't get
AST-level chunking.

## Roadmap

Versioning details live in [`docs/VERSIONING.md`](docs/VERSIONING.md).
Maintainer release flow lives in
[`docs/MAINTAINER_LOOP.md`](docs/MAINTAINER_LOOP.md).

- **v0.2.0 — shipped**: First crates.io publish, MCP tools, session dedup,
  smart outline, and expanded surface — `digest`, `impact`, `deps`, `plan`.
- **v0.3.0 — shipped**: Natural-language recall — 100-query suite across
  tokio / django / next.js, query expansion, two-stage cascade, continuous
  hybrid weighting, NDCG@10 measurement, and symbol/path component ranking.
- **v0.4.0 — active train**: Java + repo-format coverage — Java, HTML,
  prompt-first agent install, TSX grammar fixes, CSS/SCSS, Markdown/MDX,
  YAML/JSON/TOML, Dockerfile, and Shell landed; fixtures/gate hardening remain.
- **v0.5.0**: Systems + JVM tier — C, C++, Kotlin, SQL, Terraform/HCL.
- **v0.6.0**: App-framework tier — Ruby, PHP, Swift, Vue, Svelte, Astro,
  OpenAPI / GraphQL.
- **v0.7.0**: Scale + persistence — mmap index, schema versioning,
  incremental embedding re-encode, memory/disk caps.
- **v0.8.0**: Adoption + observability — adoption counter, tool-description
  A/B harness, LLM-in-loop bench, multilingual tool descriptions.
- **v0.9.0**: Workflow intelligence + ecosystem — JSON output, `diff`,
  `history`, `profile`, Aider / OpenHands / Cursor / Cline / Continue.
- **v1.0.0**: Stable default retrieval layer — stable MCP/CLI contracts,
  benchmark dashboard, release checklist, config migration, supply-chain review.

## License

MIT - See [LICENSE](LICENSE) for details.

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