Skill: anderskev/pydantic-ai-tool-system (version 1.0.1)

--- name: pydantic-ai-tool-system description: Register and implement PydanticAI tools with proper context handling, type annotations, and docstrings. Use when adding tool capabilities to agents, implementing function calling, or creating agent actions. --- # PydanticAI Tool System ## Tool Registration Two decorators based on whether you need context: ```python from pydantic_ai import Agent, RunContext agent = Agent('openai:gpt-4o') # @agent.tool - First param MUST be RunContext @agent.tool async def get_user_data(ctx: RunContext[MyDeps], user_id: int) -> str: """Get user data from database. Args: ctx: The run context with dependencies. user_id: The user's ID. """ return await ctx.deps.db.get_user(user_id) # @agent.tool_plain - NO context parameter allowed @agent.tool_plain def calculate_total(prices: list[float]) -> float: """Calculate total price. Args: prices: List of prices to sum. """ return sum(prices) ``` ## Critical Rules 1. **@agent.tool**: First parameter MUST be `RunContext[DepsType]` 2. **@agent.tool_plain**: MUST NOT have `RunContext` parameter 3. **Docstrings**: Required for LLM to understand tool purpose 4. **Google-style docstrings**: Used for parameter descriptions ### Gates (verify in the file, not from memory) 1. **Decorator matches signature** — If the first parameter is `RunContext[...]`, the decorator must be `@agent.tool` (not `@agent.tool_plain`). **Pass:** the same `def` line’s decorator stack includes `@agent.tool`, and the first parameter is typed `RunContext[...]`. 2. **Plain tools** — With `@agent.tool_plain`, the parameter list must not include `RunContext`. **Pass:** a quick scan of the signature shows no `RunContext`. 3. **Docstring for the model** — Non-empty docstring; if the tool has parameters, describe them (Google `Args:` or Sphinx `:param` when using `docstring_format='sphinx'`). **Pass:** each parameter in the signature is mentioned in the docstring body. ## Docstring Formats Google style (default): ```python @agent.tool_plain async def search(query: str, limit: int = 10) -> list[str]: """Search for items. Args: query: The search query. limit: Maximum results to return. """ ``` Sphinx style: ```python @agent.tool_plain(docstring_format='sphinx') async def search(query: str) -> list[str]: """Search for items. :param query: The search query. """ ``` ## Tool Return Types Tools can return various types: ```python # String (direct) @agent.tool_plain def get_info() -> str: return "Some information" # Pydantic model (serialized to JSON) @agent.tool_plain def get_user() -> User: return User(name="John", age=30) # Dict (serialized to JSON) @agent.tool_plain def get_data() -> dict[str, Any]: return {"key": "value"} # ToolReturn for custom content types from pydantic_ai import ToolReturn, ImageUrl @agent.tool_plain def get_image() -> ToolReturn: return ToolReturn(content=[ImageUrl(url="https://...")]) ``` ## Accessing Context RunContext provides: ```python @agent.tool async def my_tool(ctx: RunContext[MyDeps]) -> str: # Dependencies db = ctx.deps.db api = ctx.deps.api_client # Model info model_name = ctx.model.model_name # Usage tracking tokens_used = ctx.usage.total_tokens # Retry info attempt = ctx.retry # Current retry attempt (0-based) max_retries = ctx.max_retries # Message history messages = ctx.messages return "result" ``` ## Tool Prepare Functions Dynamically modify tools per-request: ```python from pydantic_ai.tools import ToolDefinition async def prepare_tools( ctx: RunContext[MyDeps], tool_defs: list[ToolDefinition] ) -> list[ToolDefinition]: """Filter or modify tools based on context.""" if ctx.deps.user_role != 'admin': # Hide admin tools from non-admins return [t for t in tool_defs if not t.name.startswith('admin_')] return tool_defs agent = Agent('openai:gpt-4o', prepare_tools=prepare_tools) ``` ## Toolsets Group and compose tools: ```python from pydantic_ai import FunctionToolset, CombinedToolset # Create a toolset db_tools = FunctionToolset() @db_tools.tool def query_users(name: str) -> list[dict]: """Query users by name.""" ... @db_tools.tool def update_user(id: int, data: dict) -> bool: """Update user data.""" ... # Use in agent agent = Agent('openai:gpt-4o', toolsets=[db_tools]) # Combine toolsets all_tools = CombinedToolset([db_tools, api_tools]) ``` ## Common Mistakes ### Wrong: Context in tool_plain ```python @agent.tool_plain async def bad_tool(ctx: RunContext[MyDeps]) -> str: # ERROR! ... ``` ### Wrong: Missing context in tool ```python @agent.tool def bad_tool(user_id: int) -> str: # ERROR! ... ``` ### Wrong: Context not first parameter ```python @agent.tool def bad_tool(user_id: int, ctx: RunContext[MyDeps]) -> str: # ERROR! ... ``` ## Async vs Sync Both work, but async is preferred for I/O: ```python # Async (preferred for I/O operations) @agent.tool async def fetch_data(ctx: RunContext[Deps]) -> str: return await ctx.deps.client.get('/data') # Sync (fine for CPU-bound operations) @agent.tool_plain def compute(x: int, y: int) -> int: return x * y ```


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