Shared from "Claude-Code" on Inkdown
The "brain" of Claude Code — how it's instructed to think, behave, and use tools.
constants/prompts.ts)The system prompt is the single most important piece of context sent to the AI model. It's built by getSystemPrompt() and structured in sections.
The prompt is split at a SYSTEM_PROMPT_DYNAMIC_BOUNDARY marker:
┌─────────────────────────────────────────────┐
│ STATIC (cached across requests) │
│ - Core instructions │
│ - Tool descriptions │
│ - Behavioral rules │
│ - Output format guidance │
├─────────────────────────────────────────────┤
│ SYSTEM_PROMPT_DYNAMIC_BOUNDARY │
├─────────────────────────────────────────────┤
│ DYNAMIC (per-session, per-request) │
│ - Environment info │
│ - Git status │
│ - MCP server info │
│ - Token budgets │
│ - Active skills │
└─────────────────────────────────────────────┘The static portion is cached by Anthropic's prompt cache (saves ~50-70K tokens of cache creation per request).
| Section | Purpose |
|---|---|
| Intro | "You are Claude Code, Anthropic's official CLI..." |
| System Rules | Core behavioral constraints (no apologies, be concise, etc.) |
| Task Guidance | How to approach coding tasks (understand → plan → execute → verify) |
| Tool Usage | How and when to use each tool |
| Tone & Style | Communication style (professional, direct, no filler) |
| Output Efficiency | Format output for terminal (code blocks, diffs, etc.) |
| Environment Info | OS, shell, project structure, git info |
| MCP Instructions | How to use MCP tools and resources |
| Scratchpad | Cross-worker file sharing instructions |
| Token Budgets | Budget constraints and warnings |
| Brief Mode | Proactive mode instructions (when enabled) |
constants/systemPromptSections.ts)Memoized/cached section factory:
// Cached section — same content across requests
systemPromptSection(id, content)
// Uncached section — changes per request
DANGEROUS_uncachedSystemPromptSection(id, content)The cache key is the section ID. When a section's content changes, the cache is invalidated.
constants/tools.ts)Defines which tools are available to different agent modes:
// Tools NOT available to any sub-agent
ALL_AGENT_DISALLOWED_TOOLS = [
'Agent', 'TeamCreate', 'TeamDelete', 'SendMessage', 'SyntheticOutput'
]
// Tools available to async (background) agents
ASYNC_AGENT_ALLOWED_TOOLS = [...]
// Tools available to in-process teammates
IN_PROCESS_TEAMMATE_ALLOWED_TOOLS = [...]
// Tools available in coordinator mode
COORDINATOR_MODE_ALLOWED_TOOLS = [...]constants/betas.ts)All Anthropic API beta header constants:
// Interleaved thinking (thinking blocks in streaming)
INTERLEAVED_THINKING_BETA = 'interleaved-thinking-2025-11-24'
// 1M token context window
CONTEXT_1M_BETA = 'context-1m-2025-09-22'
// Tool search (defer tools until needed)
TOOL_SEARCH_BETA = 'tool-search-2025-08-15'
// Fast mode (lower latency, lower quality)
FAST_MODE_BETA = 'fast-mode-2025-09-18'
// Advisor model
ADVISOR_BETA = 'advisor-2025-10-22'constants/apiLimits.ts)Hard limits for API requests:
| Resource | Limit |
|---|---|
| Image (base64) | 5MB |
| Image (dimension) | 2000px |
| PDF (pages) | 100 pages |
| PDF (raw size) | 20MB |
| Media per request | 100 items |
constants/toolLimits.ts)Output truncation limits for tools:
// Max characters for tool output before truncation
BASH_OUTPUT_MAX_CHARS = 10000
FILE_READ_MAX_CHARS = 20000
// ... etc| File | Purpose |
|---|---|
constants/prompts.ts | System prompt builder |
constants/systemPromptSections.ts | Section registry |
constants/toolsLimits.ts | Tool output limits |
constants/tools.ts | Tool availability sets |
constants/betas.ts | API beta headers |
constants/apiLimits.ts | API resource limits |
constants/common.ts | Date utilities (memoized for cache stability) |
constants/keys.ts | Keyboard key mappings |
constants/messages.ts | User-facing messages |
constants/oauth.ts | OAuth configuration |
constants/product.ts | Product metadata |
constants/figures.ts | Unicode figures/symbols |
constants/files.ts | File-related constants |
constants/github-app.ts | GitHub app config |
constants/outputStyles.ts | Output style constants |
constants/spinnerVerbs.ts | Spinner loading messages |
constants/system.ts | System-level constants |
constants/turnCompletionVerbs.ts | Turn completion indicators |
constants/xml.ts | XML tag constants |
constants/cyberRiskInstruction.ts | Security instructions |
constants/errorIds.ts | Error ID constants |