opensrc-mcp

A codemode MCP server for fetching and querying dependency source code.

Why?

Traditional MCP exposes tools directly to LLMs. This server uses the codemode pattern: agents write JavaScript that executes server-side, and only results return. Benefits:

• Context efficient - Large source trees stay server-side
• Batch operations - One call to search/read multiple files
• LLMs are better at code - More training data for JS than tool-calling

Installation

npm install -g opensrc-mcp
# or
npx opensrc-mcp

OpenCode Configuration

Add to your OpenCode config (~/.config/opencode/config.json or project opencode.json):

{
  "mcp": {
    "opensrc": {
      "type": "local",
      "command": "npx",
      "args": ["-y", "opensrc-mcp"]
    }
  }
}

Tools

search

Query fetched sources without consuming context. Data stays server-side.

// Available in sandbox:
declare const opensrc: {
  list(): Source[];
  has(name: string, version?: string): boolean;
  get(name: string): Source | undefined;
  files(sourceName: string, glob?: string): Promise<FileEntry[]>;
  grep(pattern: string, options?: {
    sources?: string[];
    include?: string;
    maxResults?: number;
  }): Promise<GrepResult[]>;
  read(sourceName: string, filePath: string): Promise<string>;
  resolve(spec: string): Promise<ParsedSpec>;
};

declare const sources: Source[];  // All fetched sources
declare const cwd: string;        // Project directory

Examples:

// List all fetched sources
async () => opensrc.list()

// Check if zod is fetched
async () => opensrc.has("zod")

// Find TypeScript files in zod
async () => opensrc.files("zod", "**/*.ts")

// Search for "parse" in zod source
async () => opensrc.grep("parse", { sources: ["zod"], include: "*.ts" })

// Read a specific file
async () => opensrc.read("zod", "src/index.ts")

execute

Mutations: fetch packages, remove, clean.

declare const opensrc: {
  fetch(specs: string | string[], options?: {
    modify?: boolean;
  }): Promise<FetchResult[]>;
  remove(names: string[]): Promise<RemoveResult>;
  clean(options?: {
    packages?: boolean;
    repos?: boolean;
    npm?: boolean;
    pypi?: boolean;
    crates?: boolean;
  }): Promise<RemoveResult>;
  readMany(sourceName: string, paths: string[]): Promise<Record<string, string>>;
};

Examples:

// Fetch npm package (auto-detects version from lockfile)
async () => opensrc.fetch("zod")

// Fetch multiple packages
async () => opensrc.fetch(["zod", "drizzle-orm", "hono"])

// Fetch GitHub repo at specific ref
async () => opensrc.fetch("vercel/ai@v3.0.0")

// Fetch from other registries
async () => opensrc.fetch("pypi:requests")
async () => opensrc.fetch("crates:serde")

// Remove a source
async () => opensrc.remove(["zod"])

// Clean all npm packages
async () => opensrc.clean({ npm: true })

// Read multiple files at once
async () => opensrc.readMany("zod", ["src/index.ts", "src/types.ts"])

Package Formats

Output Structure

Sources are stored in opensrc/ in your project:

your-project/
├── opensrc/
│   ├── sources.json     # Index of fetched sources
│   └── zod/             # Fetched source code
│       ├── src/
│       ├── package.json
│       └── ...
└── ...

How It Works

1. Agent calls execute tool with JS code: async () => opensrc.fetch("zod")
2. Code runs in sandboxed vm context with injected opensrc API
3. Server fetches package via opensrc (handles registry lookup, git clone)
4. Only the result returns to agent context

┌─────────────────────────────────────────────────────────────┐
│                      Agent Context                          │
├─────────────────────────────────────────────────────────────┤
│  Tool call: execute({ code: "async () => opensrc.fetch..." })│
│                           ↓                                 │
│  Result: { success: true, source: { name: "zod", ... } }    │
└─────────────────────────────────────────────────────────────┘
                            ↕
┌─────────────────────────────────────────────────────────────┐
│                    opensrc-mcp Server                       │
├─────────────────────────────────────────────────────────────┤
│  Sandbox executes code with injected opensrc API            │
│  Full source tree stays here, never sent to agent           │
└─────────────────────────────────────────────────────────────┘

License

MIT