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# Unofficial Relace MCP Server

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> **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** — Hybrid semantic hints + live code exploration, with stale-hint support and explicit cloud maintenance (enable with `MCP_SEARCH_RETRIEVAL=1`; choose the backend with `MCP_RETRIEVAL_BACKEND`)
- **Cloud Search** — Semantic code search over cloud-synced repositories

## Quick Start

**Prerequisites:** [uv](https://docs.astral.sh/uv/), [git](https://git-scm.com/), [ripgrep](https://github.com/BurntSushi/ripgrep) (recommended)

Using the `relace` backend (default): get your API key from [Relace Dashboard](https://app.relace.ai/settings/billing), then add to your MCP client:

<details>
<summary><strong>Cursor</strong></summary>

`~/.cursor/mcp.json`

```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"
      }
    }
  }
}
```

</details>

<details>
<summary><strong>Claude Code</strong></summary>

```bash
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
```

</details>

<details>
<summary><strong>Windsurf</strong></summary>

`~/.codeium/windsurf/mcp_config.json`

```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"
      }
    }
  }
}
```

</details>

<details>
<summary><strong>VS Code</strong></summary>

`.vscode/mcp.json`

```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}"
        }
      }
    }
  }
}
```

</details>

<details>
<summary><strong>Codex CLI</strong></summary>

`~/.codex/config.toml`

```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"
```

</details>

## Configuration

| Variable | Required | Description |
|----------|----------|-------------|
| `RELACE_API_KEY` | ✅* | API key from [Relace Dashboard](https://app.relace.ai/settings/billing); required for Relace providers and cloud tools |
| `MCP_SEARCH_RETRIEVAL` | ❌ | Set to `1` to register the `agentic_retrieval` tool |
| `MCP_RETRIEVAL_BACKEND` | ❌ | Semantic retrieval backend: `relace` (default), `codanna`, `chunkhound`, or `none` |
| `MCP_RETRIEVAL_HINT_POLICY` | ❌ | Retrieval hint policy: `prefer-stale` (default) or `strict` |
| `MCP_BACKGROUND_INDEX_MONITOR` | ❌ | Opt-in periodic refresh monitor for local indexes; requires a pinned `MCP_BASE_DIR` and a local backend |
| `MCP_BACKGROUND_INDEX_INTERVAL_SECONDS` | ❌ | Periodic local index monitor interval in seconds (default: `300`) |
| `MCP_BACKGROUND_INDEX_INITIAL_DELAY_SECONDS` | ❌ | Initial delay before the first periodic local index check in seconds (default: `30`) |
| `MCP_SEARCH_TURN_STATUS_MODE` | ❌ | Turn-status user message policy: `always` (default), `final-only`, or `off` |
| `SEARCH_BASH_TOOLS` | ❌ | Enable `bash` during search runs: `1` (on, default), `0` (off) |
| `SEARCH_LSP_TOOLS` | ❌ | Enable LSP-assisted search: `1` (on), `0` (off, default) |
| `MCP_BASE_DIR` | ❌ | Project root override (auto-detected via MCP Roots → Git → workspace storage → 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) `MCP_RETRIEVAL_BACKEND` is `codanna`, `chunkhound`, or `none`.

For `.env` usage, encoding settings, custom LLM providers, and more, see [docs/advanced.md](docs/advanced.md).

## Tools

Always available: `fast_apply`, `agentic_search`. `agentic_retrieval` requires `MCP_SEARCH_RETRIEVAL=1`. Cloud tools are available only when `MCP_RETRIEVAL_BACKEND=relace`. `index_status` is available for `relace`, `codanna`, and `chunkhound`, and hidden when `MCP_RETRIEVAL_BACKEND=none`.

Use MCP-native discovery surfaces: `list_tools()` for tools and `list_resources()` for resources.

For detailed parameters, see [docs/tools.md](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.

```bash
pip install relace-mcp[tools]
relogs
```

For detailed usage, see [docs/dashboard.md](docs/dashboard.md).

## Benchmark

Evaluate `agentic_search` performance using the [Loc-Bench](https://huggingface.co/datasets/IvanaXu/LocAgent) code localization dataset.

```bash
git clone https://github.com/possible055/relace-mcp.git
cd relace-mcp
uv sync --extra benchmark

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

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

All benchmark artifacts are written under `benchmark/.data/`.

For grid search, analysis tools, and metrics interpretation, see [docs/benchmark.md](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 or message | Solution |
|------------------|----------|
| `RELACE_API_KEY is required ...` | Set `RELACE_API_KEY` when using Relace providers or cloud tools |
| `NEEDS_MORE_CONTEXT` | Include 1-3 unique anchor lines near the target block |
| `INVALID_PATH` | Verify the path exists and is inside `MCP_BASE_DIR` or an allowed extra path |
| `FILE_TOO_LARGE` | File exceeds 10MB; split the change into smaller files or edits |
| `ENCODING_ERROR` | Set `RELACE_DEFAULT_ENCODING` explicitly for non-UTF-8 projects |
| `AUTH_ERROR` | Verify the API key and provider configuration |
| `RATE_LIMIT` | Retry later or reduce request volume |
| `NETWORK_ERROR` / `TIMEOUT_ERROR` | Check network access and retry |
| `APPLY_NOOP` | Add more specific anchors or concrete new lines so the merge can produce a diff |
| `MARKER_LEAKAGE` | Ensure placeholder markers are used only as placeholders, not expected literal output |
| `TRUNCATION_DETECTED` | Split large deletion-heavy edits or use explicit remove directives |
| `BLAST_RADIUS_EXCEEDED` | Break the change into smaller, more local edits |

## Development

```bash
git clone https://github.com/possible055/relace-mcp.git
cd relace-mcp
uv sync --extra dev --extra benchmark
uv run pytest
uv run --extra dev --extra benchmark pytest benchmark/tests -q
```

## License

MIT