Claudestine - A clandestine Claude Code reverse-engineering

A python re-implementation of Claude Code's agent system prompt generator, reverse-engineered from the official Claude Code distribution.

Overview

This package provides a faithful recreation of the prompt building system used internally by Claude Code. It includes:

• ✅ All base system prompts (interactive, SDK, non-interactive, Vertex AI)
• ✅ Built-in agent definitions (general-purpose, Explore)
• ✅ Dynamic prompt construction with environment context
• ✅ Security guidelines and safety instructions
• ✅ Comprehensive test coverage

Why

For use with the zen-mcp-server CLI Link feature, I wanted the exact system prompt used by the general purpose agent for "jailbreaking" agents to allow for recursive invocations (Agents calling agents), which is explicitly prohibited by Anthropic, who removed the feature a couple days or so after the agent feature was released.

How?

tldr; If you are curious, here are the key functions you can inspect yourself:

• jCD - Main prompt construction
• VTD - Environment context generation
• y_H - Base prompt selection
• v0$, A3 - Agent definitions

This was achieved by an "automated" analysis of Claude Code's obfuscated source. That is, in of itself, a non-trivial process involving webrack for reversing the control flow flattening (good blog) done during obfuscation (and more, but this is notable for it's impact on AST control flow graphs), followed by using babel to traverse the AST and storing the ENTIRE tree into neo4j, resulting in a data directory of about 16 GB.

From here, I used a previous project I have published, ccproxy, so that I could capture a Claude Code session and view it in LangFuse. I prompted sonnet to "Use the @agent-general purpose to say hi", and used some of the system prompt text to find the AST node containing the string:

You are an agent for Claude Code, Anthropic's official CLI for Claude. Given the user's message, you should use the tools available to complete the task. Do what has been asked; nothing more, nothing less. When you complete the task simply respond with a detailed writeup...

The full prompt goes on for several paragraphs and is dynamically generated and includes things like your git status, uname -r, working directory, recently edited files, etc.

Next, it's vibe coding time. Using the Neo4j Traversal Framework, which is much simpler for this use case than choosing Cypher, iterating on java AI slop kept Claude busy for an afternoon, traversing the AST and reconstructing the deobfuscated code using a breadth first traversal, until the size of the reconstructed code hit the 50k token limit I specified. I took this 50k token blob of deobfuscated javascript, and shoved it back into Claude, sternly ordering it to "Using python, recreate the prompt building logic for constructing system prompts", and the results speak for themselves... Wait, you don't like python?

---

Installation

uv add git+https://github.com/starbased-co/claudestine.git

Or using pip:

pip install git+https://github.com/starbased-co/claudestine.git

Quick Start

from claudestine import build_agent_prompt, get_agent, PromptBuilder

# Build a prompt for the general-purpose agent
prompts = build_agent_prompt("general-purpose")

# Access agent definitions
agent = get_agent("Explore")
print(agent.system_prompt)

# Custom prompt building
custom_prompts = PromptBuilder.build_system_prompt(
    agent=get_agent("general-purpose"),
    model="claude-sonnet-4-5-20250929",
    additional_working_dirs=["/path/to/project"],
    include_security=True
)

Features

Built-in Agents

General-Purpose Agent

from claudestine import GENERAL_PURPOSE_AGENT

# Agent optimized for:
# - Searching code across large codebases
# - Analyzing multiple files
# - Investigating complex questions
# - Multi-step research tasks

Explore Agent

from claudestine import EXPLORE_AGENT

# Agent specialized for:
# - Finding files by patterns (glob searches)
# - Searching code for keywords
# - Answering codebase structure questions

Prompt Building

from claudestine import PromptBuilder

# Build complete system prompt
prompts = PromptBuilder.build_system_prompt(
    agent=GENERAL_PURPOSE_AGENT,
    model="claude-sonnet-4-5-20250929",
    additional_working_dirs=["/home/user/project"],
    cwd="/home/user/current",
    include_security=False # the most important feature
)

# Returns list of prompt sections:
# 1. Agent's system prompt
# 2. Security guidelines (if enabled)
# 3. Notes (absolute paths, cwd reset, no emojis)
# 4. Environment context (platform, date, model info)

Environment Context

The system automatically includes:

• Current working directory
• Platform information (Linux, macOS, Windows)
• OS version (from uname)
• Today's date
• Model information with friendly names
• Additional working directories (if specified)

Dynamic Notes Section

All prompts include operational notes:

Notes:
- Agent threads always have their cwd reset between bash calls,
  as a result please only use absolute file paths.
- In your final response always share relevant file names and code snippets.
  Any file paths you return in your response MUST be absolute.
  Do NOT use relative paths.
- For clear communication with the user the assistant MUST avoid using emojis.

API Reference

build_agent_prompt(agent_type, model, **kwargs)

Build a prompt for a built-in agent.

Parameters:

• agent_type (str): Agent type ("general-purpose", "Explore")
• model (str): Model ID (e.g., "claude-sonnet-4-5-20250929")
• additional_working_dirs (list[str], optional): Additional directories
• **kwargs: Additional options passed to PromptBuilder.build_system_prompt()

Returns: list[str] - List of prompt sections

Raises: ValueError if agent_type is unknown

get_agent(agent_type)

Get a built-in agent definition.

Parameters:

• agent_type (str): Agent type

Returns: AgentDefinition | None

PromptBuilder.build_system_prompt(...)

Build a complete system prompt with all sections.

Parameters:

• agent (AgentDefinition, optional): Agent definition
• base_prompts (list[str], optional): Custom base prompts
• model (str): Model ID
• additional_working_dirs (list[str], optional): Additional directories
• cwd (str, optional): Current working directory (defaults to os.getcwd())
• mode (PromptMode): Prompt mode
• is_non_interactive (bool): Non-interactive session flag
• has_append_system_prompt (bool): SDK append flag
• include_security (bool): Include security guidelines

Returns: list[str] - List of prompt sections

Agent Definitions

Creating Custom Agents

from claudestine import AgentDefinition

custom_agent = AgentDefinition(
    agent_type="code-reviewer",
    when_to_use="Use for code review tasks",
    system_prompt="You are a code review specialist...",
    model="sonnet",
    tools=("Read", "Grep", "Glob"),
    color="blue"
)

# Build prompt for custom agent
prompts = PromptBuilder.build_system_prompt(
    agent=custom_agent,
    model="claude-sonnet-4-5-20250929"
)

Testing

# Run all tests
pytest

# Run with coverage
pytest --cov=claudestine --cov-report=html

# Run specific test
pytest tests/test_prompts.py::TestPromptBuilder

License

MIT