AI Engineering
Agentic Coding Harnesses, Compared & Explained
Master Claude Code, Aider, OpenCode, Goose, and Codex — Then Run Them Locally
A vendor-neutral, mechanism-level field guide to operating and extending agentic coding harnesses.
About this book
Coding agents now run autonomously on your behalf, searching a repository, editing files, running commands and tests, and correcting their own errors. Tools such as Claude Code, Aider, OpenCode, Goose, and Codex look very different on the surface, yet all are described with the same few words.
Agentic Coding Harnesses, Compared & Explained looks underneath. Its premise is that the intelligence lives in the model but the agency lives in the harness, the program that turns the model's requests into real actions and decides when to stop. The book follows the agent loop turn by turn, takes a harness apart into its components, and covers the infrastructure they share: the Model Context Protocol, context and cache management, and tool design and safety.
It then applies that lens to specific tools, with deep dives on Claude Code and Aider and a survey of OpenCode, Goose, and Codex, and moves on to practice: running harnesses on local models, writing project instruction files, choosing a harness per task, weighing cost against capability, and combining several harnesses in one workflow.
The book closes by building a minimal harness in Python against a scripted fake model, and by showing how to evaluate new tools as the ecosystem keeps moving. The chapters are vendor-neutral, use fictional projects, and treat specific commands and settings as conceptual sketches to verify against current documentation.
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