Ecosystem
Build an AI agent in 300 lines? Harness Engineering 101 gets a v1.1 refresh
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Harness Engineering 101
Project Oct 19, 2026
Isuru Wijesiri's 16-chapter guide to building an AI agent around a maintained conversation, with a roughly 300-line Python teaching harness.
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Harness Engineering 101 explains an agent as a program that maintains a conversation, dispatches tools and controls what the model can do. Its 16 chapters cover caching, context, background work, MCP, skills and guardrails, ending with a small Python teaching implementation. The October 19, 2026, v1.1 revision adds firsthand examples and an explicit AI usage disclosure.
The author says he drafted the chapters from experience with WSO2 copilots and One Code, a separate pi-based coding agent, and used Claude Code and One Code for editing and diagrams. The book is not itself a pi plugin. Prose is CC BY-NC-ND 4.0; Python code is MIT. The teaching harness requires an Anthropic API key and paid API usage, can execute commands, and lacks production sandboxing, retries and compaction.