The Entire Claude Code Architecture
March 31, 2026
Internal codename: Tengu. Runtime: Bun. UI: React Ink. Language: TypeScript.
1. System Overview
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2. Core Engine — The Agentic Loop
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3. Tool System
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4. Permission System
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Permission Modes
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5. Context Management — Compaction Pipeline
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Token Budget State Machine
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6. Data Flow — User Input to Response
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7. State Management
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8. Extension Model
%%{init: {'theme': 'dark', 'themeVariables': { 'primaryColor': '#1a1a2e', 'primaryTextColor': '#e0e0e0', 'lineColor': '#ffc107', 'primaryBorderColor': '#ffc107'}}}%% graph TB subgraph Skills["Skills"] BS["Bundled Skills<br/>shipped with CLI"]:::skill US["User Skills<br/>.claude/skills/*.md"]:::skill PS["Project Skills<br/>.claude/skills/ in repo"]:::skill SL["loadSkillsDir.ts<br/>discover + parse frontmatter"]:::loader end subgraph Plugins["Plugins"] MP["Managed Plugins<br/>org-level policy"]:::plugin IP["Installed Plugins<br/>user choice"]:::plugin BP["Built-in Plugins<br/>shipped with CLI"]:::plugin PL["pluginLoader.ts<br/>cache-only, versioned"]:::loader end subgraph Agents["Agents"] SA["Sub-agents via AgentTool<br/>forked context, own query loop"]:::agent CO["Coordinator Mode<br/>leader dispatches tasks,<br/>workers get limited tools"]:::agent SW["Swarms<br/>multi-process via tmux,<br/>mailbox message passing"]:::agent FA["Forked Agents<br/>share parent prompt cache,<br/>overlay filesystem"]:::agent end subgraph HookSys["Hooks"] PRE["PreToolUse<br/>before tool execution"]:::hook POST["PostToolUse<br/>after tool execution"]:::hook SESS["Session Hooks<br/>lifecycle events"]:::hook HC["Configured in<br/>settings.json or CLAUDE.md"]:::hook end CMD["commands.ts — Command Registry<br/>merges all sources"]:::registry TOOL["Tool.ts — Tool Interface"]:::registry QUERY["query.ts — Agentic Loop"]:::registry BS --> SL US --> SL PS --> SL SL --> CMD MP --> PL IP --> PL BP --> PL PL --> CMD PL -->|"plugin MCP servers"| TOOL CMD --> TOOL SA --> QUERY CO --> QUERY SW --> QUERY FA --> QUERY PRE --> TOOL POST --> TOOL HC --> PRE HC --> POST classDef skill fill:#0d4f4f,stroke:#17a2b8,color:#e0e0e0,stroke-width:2px classDef plugin fill:#2d2d0d,stroke:#ffc107,color:#e0e0e0,stroke-width:2px classDef agent fill:#2d1b4e,stroke:#6f42c1,color:#e0e0e0,stroke-width:2px classDef hook fill:#3d2b00,stroke:#fd7e14,color:#e0e0e0,stroke-width:2px classDef loader fill:#1a2d4a,stroke:#4a9eff,color:#e0e0e0,stroke-width:2px classDef registry fill:#1b3a1b,stroke:#28a745,color:#e0e0e0,stroke-width:3px
9. API Request Lifecycle
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