pkg-api-mcp

The antidote to your coding agent inventing functions that don't exist.

An MCP server that feeds Claude, Cursor, and any MCP client the real exported API surface and type signatures of any npm package — extracted straight from its published .d.ts declarations. If a function isn't in the output, the package doesn't export it. Full stop.

Why this exists

The most common way an AI coding agent wastes your time: confidently calling library.doThing(...) where doThing never existed, or passing an option the API doesn't accept. The ground truth — the package's own TypeScript declarations — is sitting on a CDN. This server puts it in the agent's context, version-pinned, before it writes the call.

Tools

Tool	What it does
package_api	The exported surface of package@version — functions, classes, consts, interfaces, types — grouped by kind with one-line signatures. Check this before calling into any unfamiliar library.
package_types	The raw .d.ts text — exact generics, overloads, and option-object shapes when a summary isn't enough.
list_type_files	Every declaration file in the package — for split types or submodule imports.

No API key. Types are read from jsDelivr, version-pinned.

Quick start

npx pkg-api-mcp

Claude Code

claude mcp add pkg-api -- npx -y pkg-api-mcp

Claude Desktop / Cursor / Windsurf / any MCP client

{
  "mcpServers": {
    "pkg-api": {
      "command": "npx",
      "args": ["-y", "pkg-api-mcp"]
    }
  }
}

Example prompts

• "What does zod@3.23.8 actually export? Use pkg-api before writing the schema."
• "Show me the real signature of format in date-fns@latest."
• "I need the exact props type for the Query client in @tanstack/react-query — pull the raw types."

Config

Env var	Default	Purpose
PKG_API_MAX_CHARS	16000	Max characters returned per call, to protect the context window.

How it works

package[@version]
   │
   ├─ jsDelivr resolve ──► exact version
   ├─ read package.json "types"/"typings" (or derive from "main")
   ├─ fetch the .d.ts from the CDN
   └─ extract every `export …` ──► grouped, signature-level API index

The extractor is deliberately dependency-free (no TypeScript compiler in your runtime) and handles functions, classes, consts, interfaces, types, enums, namespaces, export default, and export { … } from/export * re-exports.

Develop

npm install
npm run build
node dist/index.js

Caveats

• Packages that ship no types (pure JS, no bundled .d.ts) won't resolve here — their types usually live in a separate @types/<name> package; run package_api on that instead.
• The extractor is regex-based, not a full TS parse: it's built for an accurate at-a-glance index. For byte-exact overloads, use package_types.

License

MIT © Anicodeth