MCP BEYOND THE SPEC: INSIDE CODEX AND CLAUDE CODE

Summary from the TLDR IT newsletter

Popular Model Context Protocol (MCP) clients like Codex and Claude Code implement tool definitions, annotations, and search mechanisms that deviate from the base MCP specification. The schema presented to an AI model can differ significantly from the raw output provided by an MCP server due to client-side processing. The analysis involved testing specific client behaviors, including parallel execution and approval modes, to understand how they interpret MCP server data.