OpenAPI-to-MCP Turns Every API Into an Agent Tool. The Missing Piece Is Endpoint-Level Policy

OpenAPI-to-MCP gateways are gaining traction as they allow teams to swiftly convert existing APIs into tools that agents can call, enhancing delivery speed by turning endpoints into actionable tools. However, this transformation necessitates a clear understanding of the distinction between API connectivity and API authorization, as the latter involves defining the reach, authority, business intent, approvals, and audit trails for these tools. The process typically involves parsing an OpenAPI document into callable tool definitions hosted behind an MCP server endpoint, effectively turning REST endpoints into a comprehensive tool catalog that can range from low to high-risk actions, necessitating a robust risk classification and policy enforcement strategy. This approach emphasizes the importance of endpoint filtering, runtime policy evaluation, and the integration of a dedicated authorization system like Permit.io to ensure fine-grained control over tool execution. It also underscores the need for a secure runtime authorization flow that prioritizes credential safety and least privilege, backed by thorough audit records to ensure accountability and traceability of agent actions.