> ## Documentation Index
> Fetch the complete documentation index at: https://docs.usefused.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Agent Tools

> Choose server tools, client-hosted tools, MCP tools, and approval boundaries.

Agent Tools let a model act through typed, testable capabilities. Choose where each capability should run.

| Tool type      | Runs in                          | Best for                          |
| -------------- | -------------------------------- | --------------------------------- |
| `@tool`        | Agent server                     | Business logic and provider calls |
| `@client_tool` | Browser, desktop, or mobile host | UI and device capabilities        |
| MCP tool       | Remote MCP server                | External capability servers       |

## Discovery properties

| Property    | Rule                                                        |
| ----------- | ----------------------------------------------------------- |
| Location    | `tools/<name>.py`                                           |
| Export      | One callable matching the filename                          |
| Description | Docstring or decorator description                          |
| Arguments   | Structured values                                           |
| Results     | Structured values, optionally validated by Pydantic         |
| Credentials | Resolve through `context.credentials`, never tool arguments |

<CardGroup cols={2}>
  <Card title="Server tools" icon="server" href="/harnest/build/agent-tools/server-tools">
    Run typed capabilities inside the agent server.
  </Card>

  <Card title="Client-hosted tools" icon="display" href="/harnest/build/agent-tools/client-tools">
    Suspend the agent while a connected client performs local work.
  </Card>

  <Card title="Human approvals" icon="user-check" href="/harnest/build/agent-tools/human-approvals">
    Protect every tool call or one risky operation found at runtime.
  </Card>

  <Card title="MCP Client" icon="plug" href="/harnest/build/mcp-client">
    Connect the agent to tools hosted by an MCP server.
  </Card>
</CardGroup>

## Choose an approval boundary

| Need                                 | Use                               |
| ------------------------------------ | --------------------------------- |
| Every call requires permission       | `@require_human_approval`         |
| Evaluation finds one risky operation | `request_human_approval(...)`     |
| Remote operation requires permission | Approval policy on the MCP client |

Approval resumes the exact suspended task without replaying earlier work.