AI coding agents are great at writing code, but they still struggle to understand how a change affects an existing codebase. Euthynos gives them structural intelligence: who calls a function, what a change reaches, which tests matter, where similar logic exists, and how functions connect. It runs locally, is read-only and deterministic, and works through MCP with Claude Code and other agents. Euthynos matched recall while using 13–31% fewer tokens on the fully measured tasks.