# Custom Retriever (/examples/agents/knowledge/custom-retriever)



```python title="custom_retriever.py"
"""
Custom Retriever
=============================

Use knowledge_retriever to provide a custom retrieval function.

Instead of using a Knowledge instance, you can supply your own callable
that returns documents. The agent will use it as its search_knowledge_base tool.
"""

from typing import List, Optional

from agno.agent import Agent
from agno.models.openai import OpenAIResponses

# ---------------------------------------------------------------------------
# Custom Retriever Function
# ---------------------------------------------------------------------------
# A simple in-memory retriever for demonstration.
# In production, this could call an external API, database, or search engine.
DOCUMENTS = [
    {
        "title": "Python Basics",
        "content": "Python is a high-level programming language known for its readability.",
    },
    {
        "title": "TypeScript Intro",
        "content": "TypeScript adds static typing to JavaScript.",
    },
    {
        "title": "Rust Overview",
        "content": "Rust is a systems language focused on safety and performance.",
    },
]


def my_retriever(
    query: str, num_documents: Optional[int] = None, **kwargs
) -> Optional[List[dict]]:
    """Search documents by simple keyword matching."""
    query_lower = query.lower()
    results = [
        doc
        for doc in DOCUMENTS
        if query_lower in doc["content"].lower() or query_lower in doc["title"].lower()
    ]
    if num_documents:
        results = results[:num_documents]
    return results if results else None


# ---------------------------------------------------------------------------
# Create Agent
# ---------------------------------------------------------------------------
agent = Agent(
    model=OpenAIResponses(id="gpt-5.2"),
    # Use a custom retriever instead of a Knowledge instance
    knowledge_retriever=my_retriever,
    # search_knowledge is True by default when knowledge_retriever is set
    markdown=True,
)

# ---------------------------------------------------------------------------
# Run Agent
# ---------------------------------------------------------------------------
if __name__ == "__main__":
    agent.print_response(
        "Tell me about Python.",
        stream=True,
    )
```

## Run the Example [#run-the-example]

<Steps>
    <Step title="Set up your virtual environment">
      <CodeBlockTabs defaultValue="Mac">
        <CodeBlockTabsList>
          <CodeBlockTabsTrigger value="Mac">
            Mac
          </CodeBlockTabsTrigger>

          <CodeBlockTabsTrigger value="Windows">
            Windows
          </CodeBlockTabsTrigger>
        </CodeBlockTabsList>

        <CodeBlockTab value="Mac">
          ```bash
          uv venv --python 3.12
          source .venv/bin/activate
          ```
        </CodeBlockTab>

        <CodeBlockTab value="Windows">
          ```bash
          uv venv --python 3.12
          .venv\Scripts\activate
          ```
        </CodeBlockTab>
      </CodeBlockTabs>
    </Step>

  <Step title="Install dependencies">
    ```bash
    uv pip install -U agno openai
    ```
  </Step>

  <Step title="Export your OpenAI API key">
    <CodeBlockTabs defaultValue="Mac/Linux">
      <CodeBlockTabsList>
        <CodeBlockTabsTrigger value="Mac/Linux">
          Mac/Linux
        </CodeBlockTabsTrigger>

        <CodeBlockTabsTrigger value="Windows">
          Windows
        </CodeBlockTabsTrigger>
      </CodeBlockTabsList>

      <CodeBlockTab value="Mac/Linux">
        ```bash
        export OPENAI_API_KEY="your_openai_api_key_here"
        ```
      </CodeBlockTab>

      <CodeBlockTab value="Windows">
        ```bash
        $Env:OPENAI_API_KEY="your_openai_api_key_here"
        ```
      </CodeBlockTab>
    </CodeBlockTabs>
  </Step>

  <Step title="Run the example">
    Save the code above as `custom_retriever.py`, then run:

    ```bash
    python custom_retriever.py
    ```
  </Step>
</Steps>

Full source: [cookbook/02\_agents/07\_knowledge/custom\_retriever.py](https://github.com/agno-agi/agno/blob/8f36eaf2d18e91afa7b327eec66a3cd3685dcb87/cookbook/02_agents/07_knowledge/custom_retriever.py)