vstorm-co/full-stack-ai-agent-template/agent-tool

Add an Agent Tool ({{ cookiecutter.ai_framework }})

Agent tools live in backend/app/agents/tools/ and are surfaced to the model so it can call them mid-conversation. The assistant is defined in backend/app/agents/.

Steps

1. Write the tool function in backend/app/agents/tools/<tool_name>.py:

• Async, fully type-hinted, with a clear docstring — the docstring and signature are what the model sees, so make them precise.
• Pure logic: take typed args, return a JSON-serializable result. Raise on hard errors; return a structured {"error": ...} for soft failures the model should reason about.
• Keep secrets/IO behind settings and the service layer; don't inline credentials.

1. Export it from backend/app/agents/tools/__init__.py (add the import and append to __all__, matching the existing feature-gated blocks).

1. Register it on the agent in the assistant for the active framework:

{%- if cookiecutter.use_pydantic_ai %}

• app/agents/assistant.py — decorate with @agent.tool (needs RunContext[Deps]) or @agent.tool_plain (no context):

``python @agent.tool async def my_tool(ctx: RunContext[Deps], query: str) -> dict: """One-line description the model reads to decide when to call this.""" ... `` {%- elif cookiecutter.use_pydantic_deep %}

• app/agents/pydantic_deep_assistant.py — add the function to the agent's tool list.

{%- elif cookiecutter.use_langchain %}

• app/agents/langchain_assistant.py — wrap with @tool and add it to the tools=[...] passed to the agent.

{%- elif cookiecutter.use_langgraph %}

• app/agents/langgraph_assistant.py — wrap with @tool and include it in the tools list bound to the graph.

{%- elif cookiecutter.use_deepagents %}

• app/agents/deepagents_assistant.py — add the function to the agent's tool list.

{%- endif %}

1. Prompt guidance (optional but recommended): if the tool should only be used in specific situations, add a sentence to the system prompt in app/agents/prompts.py so the model knows when to reach for it.

1. Frontend rendering (optional): tool calls render as cards in the chat UI. For a bespoke card, add a renderer under frontend/src/components/chat/tool-results/; otherwise the generic card handles it.

1. Test it: add backend/tests/test_<tool_name>.py (see existing test_web_search.py / test_chart_tool.py). Tools are plain async functions — test them directly, no agent needed.

Rules

• The docstring is the contract with the model — keep it accurate and action-oriented.
• Return small, structured payloads; don't dump huge blobs into the context.
• Long-running or side-effecting work belongs in a service (and possibly a background task), not inline in the tool.
• See docs/howto/add-agent-tool.md for a fuller walkthrough.