The Loop.
Field notes for people building AI agents. In-depth, sourced, and written to be useful on a Tuesday afternoon.
How to Choose an LLM for Your AI Agent (October 2026 Edition)
A practical, data-backed guide to picking a model for agent work in October 2026, using Artificial Analysis and LMArena scores plus official list prices.
Read article →What Is an MCP Server? A Plain-English Guide, With a Free One to Try
What the Model Context Protocol is, how MCP servers work under the hood, and how to connect the free Agent Toolbox MCP server to your own agent in a few minutes.
Read article →Why Your Agent Costs More Than You Think: A Practical Guide to Tool-Calling Costs
How tool definitions, growing histories, and multi-turn loops drive the cost of AI agents, with a worked example and the caching and batching discounts that actually move the bill.
Read article →Writing tool descriptions and schemas that agents use reliably
A practical craft guide to naming tools, writing descriptions, and designing JSON schemas so language models call the right function with the right arguments.
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