Harness

Previous article: Day 5 | Tools as Interface: Built-in, Extensions, Services. Now that you know the three kinds of tools and how to pick a layer, this exercise walks you through installing a new tool with your own hands. This is an L3 exercise article. Navigation for subsequent articles: Day Type Topic 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 The Third Time You Repeat It, Make It a Tool Think about your daily routine for a second. In your agent sessions, do you keep piecing together the same bash command? Checking logs, searching rules, exporting data. Every time, the agent has to guess the parameters all over again and hit the same pitfalls. ...

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. ...

Previous article: Day 3 | Harness Hard Constraints: Static Contracts and Lifecycle Hooks. Now that we understand the principles of static contracts and Hooks, this practice session will have us apply these concepts to transform a real project. This is the L3 practice article. Navigation for subsequent articles: Day Type Topic Day 5 Backbone Tools as Interfaces: Three Extension Paths Day 6 Practice 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 Practice Graduation project: Build a team-level CI/CD automation Harness Day 10 Phase summary L3 graduation assessment + Harness future trends Have You Encountered This? On Day 3, we broke down the two-layer hard constraint mechanism of Harness: static contracts (AGENTS.md defines permission boundaries) and Hook interception (runtime inspection of every tool call). You know what an AGENTS.md looks like and why permission popups are performative security. The concepts are clear, but the moment you apply them to your own project, problems surface. ...

Previous article: Day 2 | Minimalism and Hard Isolation: The Pi Paradigm. Now that we understand why Pi strips features, we now address a more specific question: after the cuts, how should the remaining capabilities be managed? This is the backbone article of L3. Navigation for subsequent articles: Day Type Topic Day 4 Practice Rewrite your AGENTS.md + add an interception Hook Day 5 Backbone Tools as Interfaces: Three Extension Paths Day 6 Practice 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 Practice Graduation project: Build a team-level CI/CD automation Harness Day 10 Phase summary L3 graduation assessment + Harness future trends The Problem with “Allow Everything” Day 1’s miniharness had 7 tools; Day 2’s Pi cut it down to 4. Regardless of the count, they share a common premise: all tools are available by default. ...

Previous post: Day 1 | 120 Lines to Understand the Agent Loop: miniharness Teardown and 3 Counterintuitive Findings. Now that we understand the loop’s core structure, let’s ask a more fundamental question: of the remaining thousands of lines, what belongs and what doesn’t? This is an L3 core lesson. Upcoming navigation: Day Type Topic Day 3 Core Hard constraints in the Harness: static contracts and lifecycle hooks Day 4 Exercise Rewrite your AGENTS.md + add an interception hook Day 5 Core Tools as interface: three extension paths Day 6 Exercise Give your Agent a new tool Day 7 Core Meta-architecture: Everything is a Plugin Day 8 Core Memory, traces, and observability Day 9 Exercise Capstone: build a team-level CI/CD automated Harness Day 10 Wrap-up L3 graduation assessment + Harness future trends Why “More Features” Is a Reverse Optimization In Day 1 we dismantled the loop, showing that the core logic takes only about a hundred lines; the remaining thousands consist of structure, constraints, tools, permissions, and planning modes—all the extra capabilities designed to let Agents “do more things.” ...

Previous post: Day 0 | L3 Kickoff: A Short History of Harnesses, From Your Batch Script to Pi and DeepSeek Harness. Make sure you understand the Harness concept from Day 0 and the API calls from L2 Days 0-3, and let’s start dismantling the loop. This is an L3 exercise post. Upcoming navigation: Day Type Topic Day 2 Core Constraints and interception: hooks and permissions Day 3 Exercise Adding an approval gate with hooks Day 4 Core Extensions vs plugins: Pi vs DSH Day 5 Exercise Writing a Pi extension Day 6 Exercise Composing DSH Cordis plugin modes Day 7 Core Agent Teams and task DAGs Day 8 Core Memory and learning: Hermes, Nowledge Mem, EvoMap Day 9 Exercise Designing your own skill system Day 10 Wrap-up L3 graduation check Why This Is an Exercise Post The previous post traced the evolution of Harnesses. From Anthropic’s controlled experiment to the Pi and DeepSeek Harness routes, we learned one thing. Beyond the model, that guiding structure is what actually decides success. ...

Previous post: Day 16: L2 Complete! Next Stop: Harness Engineering Evolution and the L3 Blueprint. Make sure you have understood or mastered the skills Day 16 covered, and let’s start L3 from here. This is the L3 entry point. Upcoming posts: Day Type Topic Day 1 Exercise Reading the Agent Loop in 120 lines Day 2 Core Constraints and interception: hooks and permissions Day 3 Exercise Adding an approval gate with hooks Day 4 Core Extensions vs plugins: Pi vs DSH Day 5 Exercise Writing a Pi extension Day 6 Exercise Composing DSH Cordis plugin modes Day 7 Core Agent Teams and task DAGs Day 8 Core Memory and learning: Hermes, Nowledge Mem, EvoMap Day 9 Exercise Designing your own skill system Day 10 Wrap-up L3 graduation check Start by Remembering Your Day 4 Script Think back to Day 4 of L2. In that lesson we wrote a batch script: read files from a folder, call the API on each one, write the results back, and when a step failed, log the error first, then keep going. ...

This is the graduation assessment of the “AI Path: L1→L2 Upgrade Guide” series. Previous post: Part 5: How Non-Coders Use AI to Write Code. Full Navigation Day Type Topic Day 0 Core Part 1 AI Path L1→L2 Upgrade Guide (1): Your First API Call Day 1 Exercise Day 1 Exercise: Run Your First API Code Day 2 Exercise Day 2 Exercise: Run the Same Request on an Aggregator Platform Day 3 Exercise Day 3 Exercise: API Parameter Experiments Day 4 Core Part 2 AI Path L1→L2 Upgrade Guide (2): From One Call to Batch Processing: Let Your Program Do 100 Tasks Day 5 Exercise Day 5 Exercise: Teach Your Script to Read More File Formats Day 6 Exercise Day 6 Exercise: Batch Processing Practice: Pick a Scenario and Run It Day 7 Exercise Day 7 Exercise: Add Error Handling to Your Script Day 8 Core Part 3 Day 8: Autonomous AI, Automation Without Writing Code Day 9 Side Quest Day 9: API Caching Basics and Why Unit Price Isn’t the Whole Story Day 10 Exercise Day 10: Your AI Feels Like an Intern? Try the GCO Framework Day 11 Exercise Day 11: How to Verify What AI Gives You Day 12 Core Part 4 Your AI Toolbox: How Scripts and AI Agent Work Together Day 13 Exercise Day 13: Turning a Workflow into a Skill Kit Day 14 Exercise Automating Skill Documents: Four Core Blocks for Tailored AI Workflows Day 15 Core Part 5 Part 5: How Non-Coders Use AI to Write Code Day 16 Stage Recap Graduation Assessment Graduation Assessment: The L2 Nine-Item Checklist Seventeen days, from your first API call to a complete pipeline of your own. AI tools and features will keep changing, but don’t let that scare you: turning the unchanging methods and ways of thinking into your own capability is the right choice. ...