Day 5 | Tools as Interface: Built-in, Extensions, Services
Previous article: Day 4 | Rewrite Your AGENTS.md and Add Your First Interception Hook. Now that you’ve got constraints locked down, we turn to another core question: how should an Agent’s tools be designed? This is an L3 backbone article. Navigation for subsequent articles: Day Type Topic Day 6 Exercise Add a New Tool to Your Agent Day 7 Backbone Meta-Architecture: Everything is a Plugin Day 8 Backbone Memory, Traces, and Observability Day 9 Exercise Graduation Project: Build a Team-Level CI/CD Automation Harness Day 10 Phase Summary L3 Graduation Assessment + Harness Future Trends A Neglected Fact Over the first four posts we finished two phases: Day 0 built our overall understanding of Harness; Day 1 dissected the essence of the Agent Loop. Then we entered the constraint phase—Day 2 cut away what we didn’t need, Day 3 used contracts and Hooks to keep the Agent in check, and Day 4 had us actually restructure a real project. We constrained the Agent thoroughly. It stopped running wild. ...