Your agent starts out able to read files, run shell commands, and search — tools are how it reaches past that baseline to touch the outside world. Ada and Boris explain what a tool actually is, then unpack MCP, the Model Context Protocol: the open standard — think "USB for AI agents" — that lets one agent plug into any external system instead of everyone hand-wiring bespoke integrations, whether over local stdio or remote HTTP, and exposing tools, resources, and prompts. The catch: every tool's description is loaded into the context window before you type a word, so five perfectly useful tools quietly tax the counter and can make the agent slower and dumber. They close hands-on, wiring up an MCP server in Claude Code from the CLI and the .mcp.json file.
From Chapter 7 of *Harness Engineering for Vibe Coders* by J.M. Crider — hamiltonroadagility.com/vibe
## Chapters
- 0:00 — Intro- 1:43 — What a tool really is- 3:36 — MCP the universal plug- 5:43 — The hidden context tax- 7:33 — Wiring it up- 9:21 — Recap- 10:34 — Wrap-up

Knowing what belongs in an AGENTS.md and actually writing a good one are two different skills. Ada and Boris cover the four cardinal rules: keep it under sixty lines (research out of ETH Zurich found that agent-generated instruction files actually degraded performance by over twenty percent), be concrete instead of abstract, make it iterative, and don't duplicate what a linter already enforces. They walk through progressive disclosure — giving the agent the essentials up front and pointing to deeper docs only when needed — plus what never belongs (decision history, aspirational goals, personality instructions, full directory trees), and the correction-to-rule feedback loop that lets the file learn a project's failure modes from Day 1 through Month 3. They close with a quick naming note on how CLAUDE.md, AGENTS.md, and .cursorrules are the same idea under different filenames.
From Chapter 6 of *Harness Engineering for Vibe Coders* by J.M. Crider — hamiltonroadagility.com/vibe
## Chapters
- 0:00 — Intro- 1:28 — The Four Cardinal Rules- 3:17 — Progressive Disclosure- 4:56 — What Doesn't Belong- 6:39 — The Feedback Loop- 8:35 — Recap- 9:53 — Wrap-up