Prepare Tools

[PrepareTools][pydantic_ai.capabilities.PrepareTools] and [PrepareOutputTools][pydantic_ai.capabilities.PrepareOutputTools] wrap a [ToolsPrepareFunc][pydantic_ai.tools.ToolsPrepareFunc] as a capability, for filtering or modifying tool definitions per step. PrepareTools handles function tools; PrepareOutputTools handles [output tools][pydantic_ai.output.ToolOutput].

python

from pydantic_ai import Agent, RunContext, ToolDefinition
from pydantic_ai.capabilities import PrepareTools


async def hide_dangerous(ctx: RunContext, tool_defs: list[ToolDefinition]) -> list[ToolDefinition]:
    return [td for td in tool_defs if not td.name.startswith('delete_')]


agent = Agent('openai:gpt-5.2', capabilities=[PrepareTools(hide_dangerous)])


@agent.tool_plain
def delete_file(path: str) -> str:
    """Delete a file."""
    return f'deleted {path}'


@agent.tool_plain
def read_file(path: str) -> str:
    """Read a file."""
    return f'contents of {path}'


result = agent.run_sync('hello')
# The model only sees `read_file`, not `delete_file`

For more complex tool preparation logic, see Tool preparation under lifecycle hooks.