MCP includes a standard for some more advanced capabilities like: - tool discovery: for instance you can "push" an update from the server to the client, while with OpenAPI you have to wait for the client to refetch the schema - background tasks: you can have a job endpoint in your API to submit tasks and check their status, but standardization on the way to do that brings additional possibilities on the client side (imagine showing a standard progresss bar no matter which tool is being used) - streaming / incremental results / cancellation - ...

All of this is http based and could be implemented on a bespoke API but the challenge is cross-API standardization so that agents can be trained on representative data. The value of MCP is that it creates a common behavioral contract, not just a transport or schema.