Pi Web is a full-stack Next.js application that provides a browser-based interface for the Pi coding agent, an AI-powered coding assistant. It shares session files, configuration, and credential storage with the Pi CLI, enabling users to manage AI coding sessions, browse and edit files, run terminal commands, and configure models/plugins/skills—all from a web browser. The application is designed for local use, running on Node.js ≥22.19 and opening at 127.0.0.1:30141 by default. Architecturally, Pi Web is a Next.js 16 App Router application with React 19 client components, a comprehensive REST API layer, and real-time streaming via Server-Sent Events (SSE) for agent events and terminal output. It features a PWA with service worker support for push notifications and offline fallback, optional password authentication with HMAC-signed session tokens, and an extension system for custom UI widgets. The frontend is organized around a chat-centric workspace with resizable panels for session management, file viewing, terminal emulation, and configuration. Key capabilities include session lifecycle management (create, fork, rename, delete, branch), file browsing with syntax highlighting and previews (images, audio, video, PDF, DOCX), Git worktree support, subagent runtime for background tasks, model catalog configuration with provider presets, and internationalization (English, Simplified Chinese, Traditional Chinese). The codebase is extensively tested with over 100 test files using Node's test runner and jiti for TypeScript imports, covering both unit and integration tests for API routes, components, and utilities.