OpenAPI to hosted MCP without rewriting your API
Search “OpenAPI to MCP” and you’ll find SDKs, generators, and weekend projects that assume you’ll own the runtime. Most product teams don’t want another service to babysit — they want agents calling the API they already run.
The gap
MCP is the right interface for agents. Your OpenAPI is the source of truth for humans and existing clients. Bridging them usually means:
- Hand-writing tool wrappers
- Hosting a process that speaks Streamable HTTP
- Wiring auth twice (client → MCP, MCP → upstream)
- Still having no idea which calls turned into revenue
That’s a quarter of eng time for a channel that might not convert yet.
What “hosted MCP” should mean
A useful hosted layer does three things:
- Maps OpenAPI operations → MCP tools (params, body, security schemes)
- Serves a durable Streamable HTTP URL with Bearer auth
- Proxies to your base URL with your upstream secret
No second public API. No “learn MCP first” homework for the product team.
MakeCallable’s take
Paste OpenAPI JSON. Get /mcp/<publicKey>. Install in Cursor or Claude (ChatGPT needs OAuth — not in MVP). Watch the call log. When a hire, booking, or purchase closes, tag GSV.
Early access is seat-capped so support stays real. When seats fill, the waitlist captures demand instead of failing silently.
When this is not enough
You’ll still want a custom MCP server if you need exotic transports, multi-tenant OAuth broker flows, or tools that aren’t in OpenAPI. Those are later problems — after you’ve proven agents call the boring CRUD that already makes money.
Start: Quickstart · OpenAPI import