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

# Tools

> Give an Agent built-in, connected, or application-executed tools.

Tools let an Agent take action. Checkfu supports three paths, based on where the
operation runs and who owns its credential.

| Tool path          | Runs in                     | Best for                                                             |
| ------------------ | --------------------------- | -------------------------------------------------------------------- |
| **Built-in tool**  | The harness sandbox         | Files, shell commands, and capabilities the harness already provides |
| **Connected tool** | Checkfu's CapabilityGateway | Provider APIs such as GitHub, Slack, or an MCP server                |
| **Custom tool**    | Your application            | Product logic and private operations your own code should execute    |

These paths share the Agent's tool-calling interface, but they do not share an
execution or credential boundary.

## Built-in tools

`agent_toolset` scopes tools the harness already knows how to run. No Connection
or ToolSource is involved.

```json theme={"theme":{"light":"github-light","dark":"github-dark"}}
{
  "agent_toolset": {
    "default_enabled": true,
    "configs": [
      { "name": "bash", "enabled": false }
    ]
  }
}
```

Use this to narrow a harness, not to grant new provider access. The exact set
varies by HarnessProfile.

## Connected tools

A connected tool crosses Checkfu's gateway. Three resources keep the concerns
separate:

1. A **Connection** authorizes one provider account. Its credential stays in
   the selected custody boundary and is never returned to the Agent, harness,
   or sandbox.
2. A **ToolSource** discovers callable operations and their input schemas.
3. The Agent references selected tools by catalog name.

```json theme={"theme":{"light":"github-light","dark":"github-dark"}}
{
  "tools": [
    { "kind": "catalog", "name": "github.create_issue" }
  ]
}
```

Each ToolInvocation is checked against the Session's admitted Agent release, the acting
Principal's PermissionAssignments, ActionPolicies, the Connection's allowed account, and its egress
rules. A policy can deny the ToolInvocation or require an
[ActionApproval](/concepts/action-approvals) before the CapabilityGateway executes it.

<Card title="Connect a provider account" icon="link" href="/guides/connect-a-providers-account">
  Authorize an account, wait for the Connection to become healthy, and discover its tools.
</Card>

## Custom tools

A Custom tool is declared inline, but your application executes it:

```json theme={"theme":{"light":"github-light","dark":"github-dark"}}
{
  "tools": [
    {
      "kind": "custom",
      "name": "lookup_order",
      "description": "Look up an order by ID.",
      "input_schema": {
        "type": "object",
        "properties": {
          "order_id": { "type": "string" }
        },
        "required": ["order_id"]
      }
    }
  ]
}
```

When the Agent calls it, Checkfu appends `agent.tool_use` and parks the Run. Your
application reads the call, executes it, and sends `user.custom_tool_result` to
continue the same Session. Checkfu makes no outbound provider request and holds
no credential for this path.

<Card title="Serve tools from your app" icon="code" href="/guides/serve-tools-from-your-app">
  Define, sync, and execute a Custom tool with the TypeScript SDK.
</Card>

## Which path should I use?

* Use a built-in tool when the harness already owns the operation.
* Use a connected tool when Checkfu should govern the provider account and
  enforce account, approval, and egress policy, attaching the credential only
  at the trusted outbound edge.
* Use a Custom tool when the operation belongs to your application's code or
  network boundary.

An Agent can use all three at once.

## Skills

A **Skill** is not a tool. It is versioned instructions and optional files that
the Agent reads inside its sandbox. Skills have no input schema, transport, or
approval flow because nothing is being called.

```text theme={"theme":{"light":"github-light","dark":"github-dark"}}
release-notes/
  SKILL.md
  examples.md
```

Session admission pins the Skill version and content digest, so later edits do
not change an existing Session. A SkillSource can sync Skills from a Git
Project; [ship a self-authored Skill](/guides/ship-a-self-authored-skill) covers
the review and verification path.

## Advanced connections and catalogs

The [Connections and catalog](/concepts/capabilities) page covers provider
packages, OAuth and API-key custody, egress rules, source synchronization,
catalog search, enablement defaults, Skills, and proposals. You only need that
detail when you are building or governing an integration.