The Tool Interface — Why Agents Need Structured I/O
A language model produces tokens. A program takes actions. The gap between those two is the tool interface: a contract that lets the model request an action and the host execute it. Every 2026 stack — function calling on OpenAI, Anthropic, and Gemini; MCP's `tools/call`; A2A's task parts — is a different encoding of the same four-step loop. This lesson names the loop and shows the minimum machinery to run it.
Visual edition planned
This lesson isn’t interactive yet.
It is part of the curriculum and will get the same treatment as Phase 1 — a visual cover, hands-on labs, derivations with numeric checks and a quiz. Until then, the original lesson is the best place to read it:
Part of Phase 13 — Tools & Protocols. Use the previous / next cards below to keep browsing the phase.