mcp-rector-warm

Stop paying Rector's cold-start tax on every edit. A warm-process MCP server that keeps the Rector container hot. ~9× faster per call. Works with every MCP client.

Why • Install • Use it • Benchmark • Compatibility • How it works • FAQ

Why

Rector is one of the most useful tools in modern PHP — automated refactoring, type fixes, version upgrades. It is also one of the slowest to start.

Every rector process foo.php pays the same toll: autoloader bootstrap, DI container build, ruleset compile. ~3-5 seconds before a single rule fires. For agents and validators that run Rector after every edit, that cold-start cost dominates wall time.

mcp-rector-warm runs Rector inside a long-lived PHP process. First call pays the boot once. Every subsequent call reuses the live container.

Install

composer global require dpt/mcp-rector-warm

Makes mcp-rector-warm available on $PATH.

Requires PHP 8.2+. Pulls Rector ^2.4 as a real Composer dep (no phar gymnastics).

Use it

Claude Desktop

Edit ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or %APPDATA%\Claude\claude_desktop_config.json (Windows):

{
  "mcpServers": {
    "rector": {
      "command": "mcp-rector-warm",
      "args": [
        "--working-dir=/path/to/your/project",
        "--config=/path/to/your/project/rector.php"
      ]
    }
  }
}

Restart Claude. Ask: "Run Rector on src/Foo.php".

Cline / Continue / Cursor / Zed / any MCP client

Same command + args shape. The server speaks plain MCP over stdio — no client-specific glue.

Standalone

mcp-rector-warm --working-dir=/path/to/project --config=/path/to/project/rector.php

Reads MCP JSON-RPC on stdin, writes responses on stdout.

Benchmark

Measured on a real DVSI codebase (Rector config with 677 paths, ~50KB target file):

| Setup | Per-call wall | Notes | |-------|---------------|-------| | Cold rector CLI | ~4500ms | autoloader + container + ruleset each time | | mcp-rector-warm (warm) | ~500ms | container reused, opcache hot | | Daemon cold boot | ~3000ms | paid once at server start |

~9× faster per call. For a tool running Rector after 100 edits: 7.5 min → 50s.

Numbers vary with project size and rule set. The win is the cold-start amortization, not magic.

Compatibility

| Client | Status | |--------|--------| | Claude Desktop | ✅ stdio MCP | | Cline (VS Code) | ✅ stdio MCP | | Continue (VS Code / JetBrains) | ✅ stdio MCP | | Cursor | ✅ stdio MCP | | Zed | ✅ stdio MCP | | Custom (Python/Node/Go MCP clients) | ✅ standard protocol |

Any client that speaks MCP stdio works. No custom protocol.

Tools exposed

`rector_process`

Run Rector on a path.

| Argument | Type | Default | Description | |----------|------|---------|-------------| | path | string | required | Absolute path to file or directory under the working dir | | dryRun | bool | true | Preview changes only. false writes them. |

Returns:

{
  "exit_code": 0,
  "output": "...",
  "warm_boot": true
}

warm_boot: true ⇒ container reused. false ⇒ first call (cold boot just finished).

How it works

Three decisions worth knowing:

One daemon per project, not per call. Config + working dir pin at server startup. This keeps $_SERVER['argv'] clean for RectorConfigsResolver and lets the container cache across every call.
Parallel mode forcibly disabled (--debug flag). Rector's worker fork model expects $_SERVER['argv'][0] to be the rector CLI binary. From an MCP server it isn't, so workers can't respawn. Single-thread analysis only — that's fine for the per-file edit loop this is designed for.
Runtime-prefixed namespace handled. Rector's bundled Symfony is namespaced RectorPrefix<date>\\Symfony\\Component\\Console\\... to avoid dependency conflicts. The runner detects the prefix at boot and resolves Application/Input/Output class names dynamically. Survives Rector version bumps.

FAQ

Does this replace vendor/bin/rector? No. Use it from MCP clients (Claude Desktop, agents). For one-off CLI calls the regular binary is still simpler.

Does it support rector --fix? Yes — pass dryRun: false to apply changes.

Why not a phar? Rector ships as a real Composer library. Phar packaging would just add a runtime cost without a benefit here.

Memory? The daemon sets memory_limit = -1 like Rector's own CLI. Idle daemon ≈ 80MB resident.

Does it survive Rector version updates? Probably. The prefix-detection scheme is forward-compatible with new RectorPrefix<date> values. Pin a Rector version in your own composer.json if you need determinism.

Credits

Rector by Tomas Votruba and contributors — the engine doing all the real work. If you ship PHP, sponsor him.
Model Context Protocol by Anthropic — the protocol that makes this kind of tool integration possible.
mcp/sdk — official PHP SDK, used here for stdio transport + tool discovery.

Rector docs — config, rules, sets.
Rector on Packagist — the upstream package.
claude-supertool — DPT's batched-ops Claude Code companion; integrates this server as a validator.

License

Community License — see LICENSE. Built by Digital Process Tools.

MCP Servers