Direct API Wrapper
Expose an existing API as MCP tools by mapping each operation one-to-one — fastest path from 'we have an API' to 'agents can call it'.
Intent & Description
🎯 Intent
Make any well-documented API agent-callable with minimal wrapper logic.
📋 Context
You already run a stable HTTP API with an OpenAPI spec or typed SDK. You want agents to call it without re-implementing business logic or writing tool definitions by hand.
💡 Solution
Map each API operation to one MCP tool, deriving name, input schema, and output shape directly from the API contract. A generator reads the OpenAPI doc and emits the server — tools track the API automatically. FastMCP’s from_openapi/from_fastapi, fastapi-mcp, and Speakeasy/Stainless generators all follow this shape. Keep the wrapper free of new business logic so regeneration stays cheap.
Real-world Use Case
- An existing API is stable and described by an OpenAPI doc or typed SDK.
- The goal is the fastest route to making the API agent-callable.
- The API surface is small enough that one tool per operation doesn’t overwhelm the model.
- The team wants tools to track the API automatically, not be hand-maintained.
Source
📌 TL;DR
Generate MCP tools straight from your OpenAPI spec. Zero business logic in the wrapper, regenerate when the API changes. Fastest path to agent-callable.
Advantages
- Fastest path from existing API to agent-callable tool surface.
- Low maintenance — regenerate from the contract when the API changes.
- Works for any OpenAPI-described API regardless of implementation language.
- No new semantics to design or document.
Disadvantages
- Tool sprawl — a large API becomes a long list of low-level tools that overwhelms model selection.
- Programmer-oriented operation names and error shapes can mislead tool selection.
- No orchestration or error smoothing — multi-step tasks still require the model to chain calls.
- Inherits the API’s chattiness; token cost scales with round-trips.