I studied Claude Code's leaked source and built a terminal UI toolkit from it

On March 31, 2026, Claude Code's full TypeScript source was accidentally exposed via npm source maps. Like many developers, I started reading through it — and what I found surprised me. The terminal UI layer wasn't a quick hack. It was a production-grade rendering engine: a custom React reconciler, a pure TypeScript Yoga layout port, a complete ANSI/CSI/DEC/ESC/OSC parser stack, and dozens of polished UI components. All battle-tested across 500K+ daily sessions. So I extracted the architecture, rewrote the components from scratch, and turned it into an open-source toolkit. What is claude-code-kit? A terminal UI toolkit with 3 packages: @claude-code-kit/shared — Yoga layout engine (pure TypeScript, no native bindings) @claude-code-kit/ink-renderer — Terminal rendering engine (React reconciler + Flexbox + keyboard/mouse events) @claude-code-kit/ui — 25+ UI components (REPL, Select, PromptInput, Spinner, and more) Quick Start pnpm add @claude-code-kit/ui react import { render , Box , Text