OpenAPI describes an HTTP contract
An OpenAPI document maps paths, methods, inputs, outputs, servers, security schemes, and errors. It is ideal when a service already exposes a stable HTTP API or needs broad tooling compatibility.
MCP presents model-facing capabilities
MCP clients discover tools and schemas through a live protocol. Good descriptions explain selection, side effects, structured output, authorization, and operational limits.
Many services benefit from both
OpenAPI can remain the canonical web contract while MCP offers agent-native discovery and invocation. Consistent names, schemas, pricing, and limitations across both surfaces matter more than adding either label alone.