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Docs added to show how a new tool is created
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# Adding a New Tool
This guide explains how to add a new tool to the Zen MCP Server. Tools are the primary way Claude interacts with the AI models, providing specialized capabilities like code review, debugging, test generation, and more.
## Overview
The tool system in Zen MCP Server is designed to be extensible. Each tool:
- Inherits from the `BaseTool` class
- Implements required abstract methods
- Defines a request model for parameter validation
- Is registered in the server's tool registry
- Can leverage different AI models based on task requirements
## Architecture Overview
### Key Components
1. **BaseTool** (`tools/base.py`): Abstract base class providing common functionality
2. **Request Models**: Pydantic models for input validation
3. **System Prompts**: Specialized prompts that configure AI behavior
4. **Tool Registry**: Registration system in `server.py`
### Tool Lifecycle
1. Claude calls the tool with parameters
2. Parameters are validated using Pydantic
3. File paths are security-checked
4. Prompt is prepared with system instructions
5. AI model generates response
6. Response is formatted and returned
## Step-by-Step Implementation Guide
### 1. Create the Tool File
Create a new file in the `tools/` directory (e.g., `tools/example.py`):
```python
"""
Example tool - Brief description of what your tool does
This tool provides [specific functionality] to help developers [achieve goal].
Key features:
- Feature 1
- Feature 2
- Feature 3
"""
import logging
from typing import Any, Optional
from mcp.types import TextContent
from pydantic import Field
from config import TEMPERATURE_BALANCED
from systemprompts import EXAMPLE_PROMPT # You'll create this
from .base import BaseTool, ToolRequest
from .models import ToolOutput
logger = logging.getLogger(__name__)
```
### 2. Define the Request Model
Create a Pydantic model that inherits from `ToolRequest`:
```python
class ExampleRequest(ToolRequest):
"""Request model for the example tool."""
# Required parameters
prompt: str = Field(
...,
description="The main input/question for the tool"
)
# Optional parameters with defaults
files: Optional[list[str]] = Field(
default=None,
description="Files to analyze (must be absolute paths)"
)
focus_area: Optional[str] = Field(
default=None,
description="Specific aspect to focus on"
)
# You can add tool-specific parameters
output_format: Optional[str] = Field(
default="detailed",
description="Output format: 'summary', 'detailed', or 'actionable'"
)
```
### 3. Implement the Tool Class
```python
class ExampleTool(BaseTool):
"""Implementation of the example tool."""
def get_name(self) -> str:
"""Return the tool's unique identifier."""
return "example"
def get_description(self) -> str:
"""Return detailed description for Claude."""
return (
"EXAMPLE TOOL - Brief tagline describing the tool's purpose. "
"Use this tool when you need to [specific use cases]. "
"Perfect for: [scenario 1], [scenario 2], [scenario 3]. "
"Supports [key features]. Choose thinking_mode based on "
"[guidance for mode selection]. "
"Note: If you're not currently using a top-tier model such as "
"Opus 4 or above, these tools can provide enhanced capabilities."
)
def get_input_schema(self) -> dict[str, Any]:
"""Define the JSON schema for tool parameters."""
schema = {
"type": "object",
"properties": {
"prompt": {
"type": "string",
"description": "The main input/question for the tool",
},
"files": {
"type": "array",
"items": {"type": "string"},
"description": "Files to analyze (must be absolute paths)",
},
"focus_area": {
"type": "string",
"description": "Specific aspect to focus on",
},
"output_format": {
"type": "string",
"enum": ["summary", "detailed", "actionable"],
"description": "Output format type",
"default": "detailed",
},
"model": self.get_model_field_schema(),
"temperature": {
"type": "number",
"description": "Temperature (0-1, default varies by tool)",
"minimum": 0,
"maximum": 1,
},
"thinking_mode": {
"type": "string",
"enum": ["minimal", "low", "medium", "high", "max"],
"description": "Thinking depth: minimal (0.5% of model max), "
"low (8%), medium (33%), high (67%), max (100%)",
},
"continuation_id": {
"type": "string",
"description": "Thread continuation ID for multi-turn conversations",
},
},
"required": ["prompt"] + (
["model"] if self.is_effective_auto_mode() else []
),
}
return schema
def get_system_prompt(self) -> str:
"""Return the system prompt for this tool."""
return EXAMPLE_PROMPT # Defined in systemprompts/
def get_default_temperature(self) -> float:
"""Return default temperature for this tool."""
# Use predefined constants from config.py:
# TEMPERATURE_CREATIVE (0.7) - For creative tasks
# TEMPERATURE_BALANCED (0.5) - For balanced tasks
# TEMPERATURE_ANALYTICAL (0.2) - For analytical tasks
return TEMPERATURE_BALANCED
def get_model_category(self):
"""Specify which type of model this tool needs."""
from tools.models import ToolModelCategory
# Choose based on your tool's needs:
# FAST_RESPONSE - Quick responses, cost-efficient (chat, simple queries)
# BALANCED - Standard analysis and generation
# EXTENDED_REASONING - Complex analysis, deep thinking (debug, review)
return ToolModelCategory.BALANCED
def get_request_model(self):
"""Return the request model class."""
return ExampleRequest
def wants_line_numbers_by_default(self) -> bool:
"""Whether to add line numbers to code files."""
# Return True if your tool benefits from precise line references
# (e.g., code review, debugging, refactoring)
# Return False for general analysis or token-sensitive operations
return False
async def prepare_prompt(self, request: ExampleRequest) -> str:
"""
Prepare the complete prompt for the AI model.
This method combines:
- System prompt (behavior configuration)
- User request
- File contents (if provided)
- Additional context
"""
# Check for prompt.txt in files (handles large prompts)
prompt_content, updated_files = self.handle_prompt_file(request.files)
if prompt_content:
request.prompt = prompt_content
if updated_files is not None:
request.files = updated_files
# Build the prompt parts
prompt_parts = []
# Add main request
prompt_parts.append(f"=== USER REQUEST ===")
prompt_parts.append(f"Focus Area: {request.focus_area}" if request.focus_area else "")
prompt_parts.append(f"Output Format: {request.output_format}")
prompt_parts.append(request.prompt)
prompt_parts.append("=== END REQUEST ===")
# Add file contents if provided
if request.files:
# Use the centralized file handling (respects continuation)
file_content = self._prepare_file_content_for_prompt(
request.files,
request.continuation_id,
"Files to analyze"
)
if file_content:
prompt_parts.append("\n=== FILES ===")
prompt_parts.append(file_content)
prompt_parts.append("=== END FILES ===")
# Validate token limits
full_prompt = "\n".join(filter(None, prompt_parts))
self._validate_token_limit(full_prompt, "Prompt")
return full_prompt
def format_response(self, response: str, request: ExampleRequest,
model_info: Optional[dict] = None) -> str:
"""
Format the AI's response for display.
Override this to add custom formatting, headers, or structure.
The base class handles special status parsing automatically.
"""
# Example: Add a footer with next steps
return f"{response}\n\n---\n\n**Next Steps:** Review the analysis above and proceed with implementation."
```
### 4. Handle Large Prompts (Optional)
If your tool might receive large text inputs, override the `execute` method:
```python
async def execute(self, arguments: dict[str, Any]) -> list[TextContent]:
"""Override to check prompt size before processing."""
# Validate request first
request_model = self.get_request_model()
request = request_model(**arguments)
# Check if prompt is too large for MCP limits
size_check = self.check_prompt_size(request.prompt)
if size_check:
return [TextContent(type="text", text=ToolOutput(**size_check).model_dump_json())]
# Continue with normal execution
return await super().execute(arguments)
```
### 5. Create the System Prompt
Create a new file in `systemprompts/` (e.g., `systemprompts/example_prompt.py`):
```python
"""System prompt for the example tool."""
EXAMPLE_PROMPT = """You are an AI assistant specialized in [tool purpose].
Your role is to [primary responsibility] by [approach/methodology].
Key principles:
1. [Principle 1]
2. [Principle 2]
3. [Principle 3]
When analyzing content:
- [Guideline 1]
- [Guideline 2]
- [Guideline 3]
Output format:
- Start with a brief summary
- Provide detailed analysis organized by [structure]
- Include specific examples and recommendations
- End with actionable next steps
Remember to:
- Be specific and reference exact locations (file:line) when discussing code
- Provide practical, implementable suggestions
- Consider the broader context and implications
- Maintain a helpful, constructive tone
"""
```
Add the import to `systemprompts/__init__.py`:
```python
from .example_prompt import EXAMPLE_PROMPT
```
### 6. Register the Tool
#### 6.1. Import in server.py
Add the import at the top of `server.py`:
```python
from tools.example import ExampleTool
```
#### 6.2. Add to TOOLS Dictionary
Find the `TOOLS` dictionary in `server.py` and add your tool:
```python
TOOLS = {
"analyze": AnalyzeTool(),
"chat": ChatTool(),
"review_code": CodeReviewTool(),
"debug": DebugTool(),
"review_changes": PreCommitTool(),
"generate_tests": TestGenTool(),
"thinkdeep": ThinkDeepTool(),
"refactor": RefactorTool(),
"example": ExampleTool(), # Add your tool here
}
```
### 7. Write Tests
Create unit tests in `tests/test_example.py`:
```python
"""Tests for the example tool."""
import pytest
from unittest.mock import Mock, patch
from tools.example import ExampleTool, ExampleRequest
from tools.models import ToolModelCategory
class TestExampleTool:
"""Test suite for ExampleTool."""
def test_tool_metadata(self):
"""Test tool metadata methods."""
tool = ExampleTool()
assert tool.get_name() == "example"
assert "EXAMPLE TOOL" in tool.get_description()
assert tool.get_default_temperature() == 0.5
assert tool.get_model_category() == ToolModelCategory.BALANCED
def test_request_validation(self):
"""Test request model validation."""
# Valid request
request = ExampleRequest(prompt="Test prompt")
assert request.prompt == "Test prompt"
assert request.output_format == "detailed" # default
# Invalid request (missing required field)
with pytest.raises(ValueError):
ExampleRequest()
def test_input_schema(self):
"""Test input schema generation."""
tool = ExampleTool()
schema = tool.get_input_schema()
assert schema["type"] == "object"
assert "prompt" in schema["properties"]
assert "prompt" in schema["required"]
assert "model" in schema["properties"]
@pytest.mark.asyncio
async def test_prepare_prompt(self):
"""Test prompt preparation."""
tool = ExampleTool()
request = ExampleRequest(
prompt="Analyze this code",
focus_area="performance",
output_format="summary"
)
with patch.object(tool, '_validate_token_limit'):
prompt = await tool.prepare_prompt(request)
assert "USER REQUEST" in prompt
assert "Analyze this code" in prompt
assert "Focus Area: performance" in prompt
assert "Output Format: summary" in prompt
@pytest.mark.asyncio
async def test_file_handling(self):
"""Test file content handling."""
tool = ExampleTool()
request = ExampleRequest(
prompt="Analyze",
files=["/path/to/file.py"]
)
# Mock file reading
with patch.object(tool, '_prepare_file_content_for_prompt') as mock_prep:
mock_prep.return_value = "file contents"
with patch.object(tool, '_validate_token_limit'):
prompt = await tool.prepare_prompt(request)
assert "FILES" in prompt
assert "file contents" in prompt
```
### 8. Add Simulator Tests (Optional)
For tools that interact with external systems, create simulator tests in `simulator_tests/test_example_basic.py`:
```python
"""Basic simulator test for example tool."""
from simulator_tests.base_test import SimulatorTest
class TestExampleBasic(SimulatorTest):
"""Test basic example tool functionality."""
def test_example_analysis(self):
"""Test basic analysis with example tool."""
result = self.call_tool(
"example",
{
"prompt": "Analyze the architecture of this codebase",
"model": "flash",
"output_format": "summary"
}
)
self.assert_tool_success(result)
self.assert_content_contains(result, ["architecture", "summary"])
```
### 9. Update Documentation
Add your tool to the README.md in the tools section:
```markdown
### Available Tools
- **example** - Brief description of what the tool does
- Use cases: [scenario 1], [scenario 2]
- Supports: [key features]
- Best model: `balanced` category for standard analysis
```
## Advanced Features
### Understanding Conversation Memory
The `continuation_id` feature enables multi-turn conversations using the conversation memory system (`utils/conversation_memory.py`). Here's how it works:
1. **Thread Creation**: When a tool wants to enable follow-up conversations, it creates a thread
2. **Turn Storage**: Each exchange (user/assistant) is stored as a turn with metadata
3. **Cross-Tool Continuation**: Any tool can continue a conversation started by another tool
4. **Automatic History**: When `continuation_id` is provided, the full conversation history is reconstructed
Key concepts:
- **ThreadContext**: Contains all conversation turns, files, and metadata
- **ConversationTurn**: Single exchange with role, content, timestamp, files, tool attribution
- **Thread Chains**: Conversations can have parent threads for extended discussions
- **Turn Limits**: Default 20 turns (configurable via MAX_CONVERSATION_TURNS)
Example flow:
```python
# Tool A creates thread
thread_id = create_thread("analyze", request_data)
# Tool A adds its response
add_turn(thread_id, "assistant", response, files=[...], tool_name="analyze")
# Tool B continues the same conversation
context = get_thread(thread_id) # Gets full history
# Tool B sees all previous turns and files
```
### Supporting Special Response Types
Tools can return special status responses for complex interactions. These are defined in `tools/models.py`:
```python
# Currently supported special statuses:
SPECIAL_STATUS_MODELS = {
"need_clarification": NeedClarificationModel,
"focused_review_required": FocusedReviewRequiredModel,
"more_review_required": MoreReviewRequiredModel,
"more_testgen_required": MoreTestGenRequiredModel,
"more_refactor_required": MoreRefactorRequiredModel,
"resend_prompt": ResendPromptModel,
}
```
Example implementation:
```python
# In your tool's format_response or within the AI response:
if need_clarification:
return json.dumps({
"status": "need_clarification",
"questions": ["What specific aspect should I focus on?"],
"context": "I need more information to proceed"
})
# For custom review status:
if more_analysis_needed:
return json.dumps({
"status": "focused_review_required",
"files": ["/path/to/file1.py", "/path/to/file2.py"],
"focus": "security",
"reason": "Found potential SQL injection vulnerabilities"
})
```
To add a new custom response type:
1. Define the model in `tools/models.py`:
```python
class CustomStatusModel(BaseModel):
"""Model for custom status responses"""
status: Literal["custom_status"]
custom_field: str
details: dict[str, Any]
```
2. Register it in `SPECIAL_STATUS_MODELS`:
```python
SPECIAL_STATUS_MODELS = {
# ... existing statuses ...
"custom_status": CustomStatusModel,
}
```
3. The base tool will automatically handle parsing and validation
### Token Management
For tools processing large amounts of data:
```python
# Calculate available tokens dynamically
def prepare_large_content(self, files: list[str], remaining_budget: int):
# Reserve tokens for response
reserve_tokens = 5000
# Use model-specific limits
effective_max = remaining_budget - reserve_tokens
# Process files with budget
content = self._prepare_file_content_for_prompt(
files,
continuation_id,
"Analysis files",
max_tokens=effective_max,
reserve_tokens=reserve_tokens
)
```
### Web Search Integration
Enable web search for tools that benefit from current information:
```python
# In prepare_prompt:
websearch_instruction = self.get_websearch_instruction(
request.use_websearch,
"""Consider searching for:
- Current best practices for [topic]
- Recent updates to [technology]
- Community solutions for [problem]"""
)
full_prompt = f"{system_prompt}{websearch_instruction}\n\n{user_content}"
```
## Best Practices
1. **Clear Tool Descriptions**: Write descriptive text that helps Claude understand when to use your tool
2. **Proper Validation**: Use Pydantic models for robust input validation
3. **Security First**: Always validate file paths are absolute
4. **Token Awareness**: Handle large inputs gracefully with prompt.txt mechanism
5. **Model Selection**: Choose appropriate model category for your tool's complexity
6. **Line Numbers**: Enable for tools needing precise code references
7. **Error Handling**: Provide helpful error messages for common issues
8. **Testing**: Write comprehensive unit tests and simulator tests
9. **Documentation**: Include examples and use cases in your description
## Common Pitfalls to Avoid
1. **Don't Skip Validation**: Always validate inputs, especially file paths
2. **Don't Ignore Token Limits**: Use `_validate_token_limit` and handle large prompts
3. **Don't Hardcode Models**: Use model categories for flexibility
4. **Don't Forget Tests**: Every tool needs tests for reliability
5. **Don't Break Conventions**: Follow existing patterns from other tools
## Testing Your Tool
### Manual Testing
1. Start the server with your tool registered
2. Use Claude Desktop to call your tool
3. Test various parameter combinations
4. Verify error handling
### Automated Testing
```bash
# Run unit tests
pytest tests/test_example.py -xvs
# Run all tests to ensure no regressions
pytest -xvs
# Run simulator tests if applicable
python communication_simulator_test.py
```
## Checklist
Before submitting your PR:
- [ ] Tool class created inheriting from `BaseTool`
- [ ] All abstract methods implemented
- [ ] Request model defined with proper validation
- [ ] System prompt created in `systemprompts/`
- [ ] Tool registered in `server.py`
- [ ] Unit tests written and passing
- [ ] Simulator tests added (if applicable)
- [ ] Documentation updated
- [ ] Code follows project style (ruff, black, isort)
- [ ] Large prompt handling implemented (if needed)
- [ ] Security validation for file paths
- [ ] Appropriate model category selected
- [ ] Tool description is clear and helpful
## Example: Complete Simple Tool
Here's a minimal but complete example tool:
```python
"""
Simple calculator tool for mathematical operations.
"""
from typing import Any, Optional
from mcp.types import TextContent
from pydantic import Field
from config import TEMPERATURE_ANALYTICAL
from .base import BaseTool, ToolRequest
from .models import ToolOutput
class CalculateRequest(ToolRequest):
"""Request model for calculator tool."""
expression: str = Field(
...,
description="Mathematical expression to evaluate"
)
class CalculatorTool(BaseTool):
"""Simple calculator tool."""
def get_name(self) -> str:
return "calculate"
def get_description(self) -> str:
return (
"CALCULATOR - Evaluates mathematical expressions. "
"Use this for calculations, conversions, and math problems."
)
def get_input_schema(self) -> dict[str, Any]:
schema = {
"type": "object",
"properties": {
"expression": {
"type": "string",
"description": "Mathematical expression to evaluate",
},
"model": self.get_model_field_schema(),
},
"required": ["expression"] + (
["model"] if self.is_effective_auto_mode() else []
),
}
return schema
def get_system_prompt(self) -> str:
return """You are a mathematical assistant. Evaluate the expression
and explain the calculation steps clearly."""
def get_default_temperature(self) -> float:
return TEMPERATURE_ANALYTICAL
def get_request_model(self):
return CalculateRequest
async def prepare_prompt(self, request: CalculateRequest) -> str:
return f"Calculate: {request.expression}\n\nShow your work step by step."
```
## Need Help?
- Look at existing tools (`chat.py`, `refactor.py`) for examples
- Check `base.py` for available helper methods
- Review test files for testing patterns
- Ask questions in GitHub issues if stuck