callspec

Define your API once with simple TypeScript — methods like getProductById with typed inputs, outputs, and errors — and Callspec gives you the whole stack from that one place: the server, a TypeScript SDK you use in your own app or ship to consumers, shared types (and optional form validators), docs, MCP tools, and OpenAPI 3.1.

On the frontend you call api.getProductById({…}) and get a Result back — success value or a typed error code you can switch on. Same methods, same types, same errors as the server and as agents on MCP. No drift, no hand-rolled client, no guessing which status codes mean what.

• 🧪 Unit-test the real handler — .handler(input, ctx) — no HTTP, no req/res, no mocks (unless you use singletons); 100% line/branch/function coverage is realistic

• 🎯 Result-typed errors — end-to-end error codes from handler → SDK → OpenAPI → MCP

• 🤖 MCP from the same routes — your TypeScript API is also a Cursor/Claude tool server

• ⚡ RPC functions — define simple functions like getProductById, not REST CRUD

• 🧩 TypeScript SDK — use it in your frontend or publish it for API consumers

• 📄 OpenAPI 3.1 — for tooling, gateways, and multi-language generators when you need them

• 📘 Docs UI — white-label explorer to try methods and connect MCP clients

• ✅ Shared types & schemas — same preds end-to-end; optional exports land on generated schemas

Try the demo

Hosted (browse routes / MCP connect snippets): callspec.logfox.ai/demo

Live try-it + MCP locally:

git clone https://github.com/logfoxai/callspec.git
cd callspec && npm install
npm run build && npm run serve:chirp-demo

Open http://127.0.0.1:3456/v1/docs — fictional Chirp API v2. Bearer token demo for authenticated routes and MCP.

Related MCP server: Graft

Contents

For coding agents: Working with Coding Agents (copy-paste skill + prompts). Skill file: SKILL.md.

• Getting started

• Working with Coding Agents

• Server layout

• Unit testing

• Single-file server example

• Authentication

• Request context

• API reference — Handlers

• Error handling

• Builtin errors

• SDK generation

• Client usage

• Shared validation

• Docs UI

• Docs UI branding (theme vars, logos, links, notice)

• Hosting Docs UI (CloudFront / Pages)

• MCP Server

• OpenAPI

• Multi-language SDKs

• Development