Inside OpenCode: How an AI Coding Agent Works

Inside OpenCode: How an AI Coding Agent Works >--- You've used AI coding tools. But do you know how they actually work? Inside OpenCode is the first book to crack open a production AI coding agent and walk you through every layer - from the CLI entry point to the agentic loop, from tool execution to stream processing, from permission systems to context compaction. OpenCode is the open-source AI coding agent built by the team at Anomaly. It connects to 20+ LLM providers, executes multi-step tool chains autonomously, and runs entirely in your terminal. This book traces every line of its TypeScript source, showing you exactly how a natural-language prompt becomes working code.What You'll Learn >Tool Architecture - How 22 built-in tools (file read/write/edit, bash execution, web fetch, code search, sub-agent spawning) are registered, permission-checked, and executed. How MCP extends the tool set at runtime. Provider Abstraction - One interface, twenty backends. How a model ID string like `anthropic/claude-sonnet-4-20250514` is resolved through fuzzy matching, config overrides, and the Vercel AI SDK into a callable language model. Stream Processing - How raw LLM token streams are parsed into structured parts, how tool calls are detected mid-stream, and how events flow through the bus to drive real-time UI updates. The Full Stack - Bootstrap and project discovery. Configuration merging. Session persistence in SQLite. Snapshot-based git change tracking. Context compaction when conversations grow too long. Permission rules that balance autonomy with safety.Who This Book Is For - Engineers building AI-powered tools who want a complete, working reference architecture - Developers curious about what happens inside tools like Claude Code, Cursor, and GitHub Copilot - Contributors to OpenCode who need a deep understanding of the codebase - Technical leaders evaluating AI agents who want to understand the engineering behind the capabilitiesWhat Makes This Book Different >The book covers 33 chapters across eight parts - from orientation and startup through providers, sessions, the prompt-to-response loop, tools, supporting infrastructure, and client interfaces. Each chapter includes a source file map and test references so you can follow along in the code. 33 chapters - 8 parts - 100% open source