Core File Index

Note

This index lists the approximately 50 most architecturally significant source files in Claude Code’s codebase, organized by module. File sizes and line counts are approximate based on analysis of the open-source repository. Paths are relative to the repository root.

Entry & Bootstrap

Path	~Lines	Responsibility
cli/src/index.ts	150	CLI entry point, argument parsing, process setup
cli/src/main.ts	300	Bootstrap sequence: config loading → auth → agent initialization
cli/src/cli.ts	250	Commander.js command definitions, flag parsing
cli/src/constants.ts	200	Global constants: model names, timeouts, limits

Configuration

Path	~Lines	Responsibility
cli/src/config/config.ts	400	Multi-source configuration merging (flags > env > project > user > defaults)
cli/src/config/schema.ts	350	Zod schemas for all configuration options
cli/src/config/claudeMd.ts	200	CLAUDE.md file discovery and parsing (project → user → enterprise hierarchy)
cli/src/config/settings.ts	250	Settings persistence and .claude/settings.json management

Agentic Loop

Path	~Lines	Responsibility
cli/src/agent/agent.ts	500	Core agent class: manages the conversation loop lifecycle
cli/src/agent/agentLoop.ts	600	The async generator loop: LLM call → tool dispatch → result collection → repeat
cli/src/agent/turn.ts	400	Single turn processing: stream handling, tool extraction, stop condition checking
cli/src/agent/stopConditions.ts	200	Stop condition evaluation: end_turn, max_tokens, tool_use, error states
cli/src/agent/costTracker.ts	300	Token counting, cost calculation, budget enforcement

Tool System

Path	~Lines	Responsibility
cli/src/tools/toolRegistry.ts	350	Central tool registry: registration, lookup, schema validation
cli/src/tools/toolExecutor.ts	400	Tool execution orchestration: permission check → execute → format result
cli/src/tools/streamingToolExecutor.ts	500	Streaming tool executor: parse partial JSON, execute before stream ends
cli/src/tools/toolDefinitions.ts	300	Tool schema definitions for API (names, descriptions, input schemas)
cli/src/tools/impl/readFile.ts	250	ReadFile tool: file reading with encoding detection, line limiting
cli/src/tools/impl/writeFile.ts	350	WriteFile/Edit tool: file writing with diff generation, backup
cli/src/tools/impl/bash.ts	600	Bash tool: shell command execution with streaming output
cli/src/tools/impl/glob.ts	200	Glob tool: file pattern matching with gitignore respect
cli/src/tools/impl/grep.ts	250	Grep tool: content search with regex support, context lines
cli/src/tools/impl/webSearch.ts	200	WebSearch tool: web search integration
cli/src/tools/impl/webFetch.ts	250	WebFetch tool: URL fetching with HTML-to-markdown conversion
cli/src/tools/impl/todoWrite.ts	200	TodoWrite tool: structured task list management
cli/src/tools/impl/notebookEdit.ts	300	NotebookEdit tool: Jupyter notebook cell manipulation

Agent Coordination

Path	~Lines	Responsibility
cli/src/agent/fork.ts	400	Fork mechanism: spawn parallel independent sub-agents
cli/src/agent/coordinator.ts	500	Coordinator pattern: task planning, worker management, replanning
cli/src/agent/team.ts	450	Team/Swarm pattern: peer agents, mailbox communication
cli/src/agent/subAgent.ts	300	Sub-agent factory: create child agents with shared context prefix
cli/src/agent/worktree.ts	250	Git worktree management for agent isolation
cli/src/agent/mailbox.ts	200	Shared message queue for team communication

Context Engine

Path	~Lines	Responsibility
cli/src/context/systemPrompt.ts	500	System prompt assembly: identity + capabilities + project context
cli/src/context/promptCache.ts	300	Prompt cache optimization: prefix ordering, cache breakpoint placement
cli/src/context/compression.ts	600	Four-layer compression pipeline: snip → microcompact → auto compact → truncate
cli/src/context/memory.ts	350	Memory system: conversation history management, message formatting
cli/src/context/tokenCounter.ts	200	Token counting utilities: cl100k estimation, budget tracking

Permission & Security

Path	~Lines	Responsibility
cli/src/security/permissionManager.ts	400	Permission orchestration: check tool → apply rules → prompt user
cli/src/security/bashSecurity.ts	800	Bash 27-layer security: AST analysis, semantic checks, path validation
cli/src/security/ruleEngine.ts	350	Rule matching engine: pattern-based allow/deny rules from multiple sources
cli/src/security/pathValidator.ts	250	Path validation: project boundary enforcement, symlink resolution
cli/src/security/threatDetector.ts	300	Threat detection: obfuscation, injection, privilege escalation patterns

Streaming Infrastructure

Path	~Lines	Responsibility
cli/src/streaming/sseParser.ts	300	Server-Sent Events parser: raw bytes → typed stream events
cli/src/streaming/apiStream.ts	400	API streaming client: connection management, reconnection, abort handling
cli/src/streaming/jsonParser.ts	250	Incremental JSON parser: partial JSON → complete values for early tool execution

UI Layer

Path	~Lines	Responsibility
cli/src/ui/App.tsx	400	Root Ink component: layout, theme, global state
cli/src/ui/MessageDisplay.tsx	350	Message rendering: markdown, code blocks, tool results
cli/src/ui/ToolOutput.tsx	250	Tool execution display: spinner, progress, result formatting
cli/src/ui/PermissionPrompt.tsx	200	Permission dialog: tool details, allow/deny/always options
cli/src/ui/InputArea.tsx	300	User input: multiline editing, history, slash commands

MCP Integration

Path	~Lines	Responsibility
cli/src/mcp/mcpClient.ts	400	MCP client: connection lifecycle, tool discovery, request routing
cli/src/mcp/mcpToolAdapter.ts	250	Adapts MCP tool schemas to Claude Code’s internal tool format
cli/src/mcp/mcpConfig.ts	200	MCP server configuration: discovery, connection settings

Hooks & Extensions

Path	~Lines	Responsibility
cli/src/hooks/hookRunner.ts	300	Hook execution engine: event matching, script execution, timeout management
cli/src/hooks/hookConfig.ts	200	Hook configuration loading from .claude/hooks.json
cli/src/plugins/pluginLoader.ts	250	Plugin discovery and loading: dynamic import, registration

Summary Statistics

Module	Files Listed	~Total Lines	% of Core
Entry & Bootstrap	4	900	3%
Configuration	4	1,200	5%
Agentic Loop	5	2,000	8%
Tool System	13	4,200	16%
Agent Coordination	6	2,100	8%
Context Engine	5	1,950	7%
Permission & Security	5	2,100	8%
Streaming	3	950	4%
UI Layer	5	1,500	6%
MCP	3	850	3%
Hooks & Extensions	3	750	3%
Total (top 56 files)	56	~18,500	~4% of 512K

The 4% Rule

The top ~56 files represent roughly 4% of the total codebase but contain nearly all of the core architectural logic. The remaining 96% consists of tests, tool implementations (repetitive per-tool boilerplate), type definitions, utilities, and build configuration. To understand Claude Code’s architecture, you only need to read these 56 files.