English | 简体中文

Unofficial Relace MCP Server

Unofficial — Personal project, not affiliated with Relace.

Built with AI — Developed entirely with AI assistance (Antigravity, Codex, Cursor, Github Copilot, Windsurf).

MCP server providing AI-powered code editing and intelligent codebase exploration tools.

Without	With `agentic_search` + `fast_apply`
Manual grep, misses related files	Ask naturally, get precise locations
Edits break imports elsewhere	Traces imports and call chains
Full rewrites burn tokens	Describe changes, no line numbers
Line number errors corrupt code	10,000+ tokens/sec merging

Features

Fast Apply — Apply code edits at 10,000+ tokens/sec via Relace API
Agentic Search — Agentic codebase exploration with natural language queries
Agentic Retrieval — Two-stage semantic + agentic code retrieval (requires MCP_SEARCH_RETRIEVAL=1)
Cloud Search — Semantic code search over cloud-synced repositories

Quick Start

Prerequisites: uv, git, ripgrep (recommended)

Using Relace (default) or RELACE_CLOUD_TOOLS=1: get your API key from Relace Dashboard, then add to your MCP client:

Cursor

~/.cursor/mcp.json

{
  "mcpServers": {
    "relace": {
      "command": "uv",
      "args": ["tool", "run", "relace-mcp"],
      "env": {
        "RELACE_API_KEY": "rlc-your-api-key",
        "MCP_BASE_DIR": "/absolute/path/to/your/project"
      }
    }
  }
}

Claude Code

claude mcp add relace \
  --env RELACE_API_KEY=rlc-your-api-key \
  --env MCP_BASE_DIR=/absolute/path/to/your/project \
  -- uv tool run relace-mcp

Windsurf

~/.codeium/windsurf/mcp_config.json

{
  "mcpServers": {
    "relace": {
      "command": "uv",
      "args": ["tool", "run", "relace-mcp"],
      "env": {
        "RELACE_API_KEY": "rlc-your-api-key",
        "MCP_BASE_DIR": "/absolute/path/to/your/project"
      }
    }
  }
}

VS Code

.vscode/mcp.json

{
  "mcp": {
    "servers": {
      "relace": {
        "type": "stdio",
        "command": "uv",
        "args": ["tool", "run", "relace-mcp"],
        "env": {
          "RELACE_API_KEY": "rlc-your-api-key",
          "MCP_BASE_DIR": "${workspaceFolder}"
        }
      }
    }
  }
}

Codex CLI

~/.codex/config.toml

[mcp_servers.relace]
command = "uv"
args = ["tool", "run", "relace-mcp"]

[mcp_servers.relace.env]
RELACE_API_KEY = "rlc-your-api-key"
MCP_BASE_DIR = "/absolute/path/to/your/project"

Configuration

Variable	Required	Description
`RELACE_API_KEY`	✅*	API key from Relace Dashboard
`RELACE_CLOUD_TOOLS`	❌	Set to `1` to enable cloud tools
`MCP_SEARCH_RETRIEVAL`	❌	Set to `1` to enable `agentic_retrieval` tool
`SEARCH_LSP_TOOLS`	❌	LSP tools: `1` (all on), `auto` (detect installed servers), `0` (off, default)
`MCP_BASE_DIR`	❌	Project root (auto-detected via MCP Roots → Git → CWD)
`MCP_LOGGING`	❌	File logging: `off` (default), `safe`, `full`
`MCP_DOTENV_PATH`	❌	Path to `.env` file for centralized config

* Optional if both: (1) APPLY_PROVIDER and SEARCH_PROVIDER are non-Relace providers, and (2) RELACE_CLOUD_TOOLS=false.

For .env usage, encoding settings, custom LLM providers, and more, see docs/advanced.md.

Tools

Core tools (fast_apply, agentic_search) are always available. Cloud tools require RELACE_CLOUD_TOOLS=1. agentic_retrieval requires MCP_SEARCH_RETRIEVAL=1.

For detailed parameters, see docs/tools.md.

Language Support

LSP tools use external language servers installed on your system.

Language	Language Server	Install Command
Python	basedpyright	(bundled)
TypeScript/JS	typescript-language-server	`npm i -g typescript-language-server typescript`
Go	gopls	`go install golang.org/x/tools/gopls@latest`
Rust	rust-analyzer	`rustup component add rust-analyzer`

Dashboard

Real-time terminal UI for monitoring operations.

pip install relace-mcp[tools]
relogs

For detailed usage, see docs/dashboard.md.

Benchmark

Evaluate agentic_search performance using the Loc-Bench code localization dataset.

# Install benchmark dependencies
pip install relace-mcp[benchmark]

# Build dataset from Hugging Face
uv run python -m benchmark.cli.build_locbench --output artifacts/data/raw/locbench_v1.jsonl

# Run evaluation
uv run python -m benchmark.cli.run --dataset artifacts/data/raw/locbench_v1.jsonl --limit 20

For grid search, analysis tools, and metrics interpretation, see docs/benchmark.md.

Platform Support

Platform	Status	Notes
Linux	✅ Fully supported	Primary development platform
macOS	✅ Fully supported	All features available
Windows	⚠️ Partial	`bash` tool unavailable; use WSL for full functionality

Troubleshooting

Error	Solution
`RELACE_API_KEY is not set`	Set the key in your environment or MCP config
`NEEDS_MORE_CONTEXT`	Include 1–3 anchor lines before/after target block
`FILE_TOO_LARGE`	File exceeds 10MB; split file
`ENCODING_ERROR`	Set `RELACE_DEFAULT_ENCODING` explicitly
`AUTH_ERROR`	Verify API key is valid and not expired
`RATE_LIMIT`	Too many requests; wait and retry
`CONNECTION_TIMEOUT`	Check network connection or increase timeout setting
`INVALID_PATH`	File path doesn't exist or no permission; verify path and access rights
`SYNTAX_ERROR`	Invalid edit_snippet format; ensure placeholder syntax is correct
`NO_MATCH_FOUND`	No search results; try broader query or run `cloud_sync` first
`CLOUD_NOT_SYNCED`	Repository not synced to Relace Cloud; run `cloud_sync` first
`CONFLICT_DETECTED`	Edit conflict; file was modified, re-read before editing

Development

git clone https://github.com/possible055/relace-mcp.git
cd relace-mcp
uv sync --extra dev
uv run pytest

License

MIT