anthropic-sdk agent-loop tool-use implementation typescript

Build agent loops directly with Anthropic SDK

The agentic pattern is a ~40-line loop: call the model, run requested tools, feed results back, repeat until stop_reason !== "tool_use" — skip framework overhead entirely.

June 5, 2026

Summary

Eliminates confusion between Claude Code (Anthropic's CLI) and DIY agents built on the SDK. Gives developers a concrete, minimal implementation to own rather than inheriting black-box framework assumptions.

Why it matters

Implementation verdict

Replaces agent framework abstractions with explicit loop control. Requires understanding the four key patterns (append assistant turn verbatim, match tool_use_id, batch results in single user message, cap iterations). Ready now — author provides MIT-licensed Next.js starter (AgentLoop) deployable in one command.

Sources

1.the agentic CLI, CLAUDE.md files, slash commands, hooks
2.Most "agent frameworks" just hide that loop from you. It's small enough that you don't need them.
3.The four things people get wrong: Append the assistant turn verbatim — so the model sees its own tool request on the next call.
4.One tool_result per request, matched by tool_use_id.
5.Send all results back in a single user message.
6.Cap the turns so a confused model can't loop forever.
7.the whole agent in ~150 readable lines, no framework

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