Developer builds open-source security layer for MCP tool servers used by AI agents

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Model Context Protocol (MCP), used by AI tools like Claude Desktop and Cursor to connect agents to external services, has no built-in security model — leaving authentication, authorization, and audit logging entirely to developers. A developer identified critical gaps including plaintext credential storage, lack of read/write scoping, and untracked tool calls that could modify or delete data without any record. To address this, they built Heddle, an open-source runtime that sits between a YAML config file and the MCP protocol, enforcing security policies on every tool call. Heddle routes each call through a six-layer pipeline covering rate limiting, access mode checks, trust tier enforcement, input validation, and more. The project was motivated by a real misconfiguration the developer caught during testing, where a supposedly read-only agent had access to a write-capable HTTP tool that would otherwise have gone undetected.

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