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

# Tools and Approvals

> Define local, external, and approval-gated tools in the Rust Agent SDK.

## Local tools

Use `Tool::new(...)` when the Rust process can execute the operation:

```rust theme={null}
use phaseo_agent::Tool;
use serde_json::json;

let get_status = Tool::new(
    "get_status",
    "Get the current service status",
    json!({
        "type": "object",
        "properties": {
            "service": { "type": "string" }
        },
        "required": ["service"]
    }),
    |input, _context| {
        Ok(json!({
            "service": input["service"],
            "status": "healthy"
        }))
    },
);
```

The parameters value is sent to the model as JSON Schema. Tool input and output are `serde_json::Value`; validate untrusted arguments inside the executor when stronger runtime guarantees are required.

## Approval-gated tools

Add `require_approval()` to pause before execution:

```rust theme={null}
let deploy = Tool::new(
    "deploy",
    "Deploy an application environment",
    json!({
        "type": "object",
        "properties": {
            "environment": { "type": "string" }
        },
        "required": ["environment"]
    }),
    |input, _context| {
        Ok(json!({
            "environment": input["environment"],
            "deployed": true
        }))
    },
)
.require_approval();
```

When the model calls this tool, the run returns with `run.status == "waiting_for_human"` and `run.pause.kind == "tool_approval"`.

Resume by exact call ID:

```rust theme={null}
use phaseo_agent::{ContinueOptions, ToolDecision};

let approvals = paused.run.pause.as_ref().unwrap()
    .pending_tool_calls
    .iter()
    .map(|pending| ToolDecision {
        tool_call_id: pending.call.id.clone(),
        reason: Some("Approved by the release operator".to_string()),
    })
    .collect();

let mut options = ContinueOptions::new(paused);
options.approvals = approvals;

let completed = agent.continue_run(&mut client, options)?;
```

The Rust `0.1` API does not expose a separate rejection type. Leave an unapproved call paused or apply your application's rejection policy before resuming.

## External tools

Use `Tool::external(...)` when another process performs the operation:

```rust theme={null}
let ticket_lookup = Tool::external(
    "ticket_lookup",
    "Load one support ticket",
    json!({
        "type": "object",
        "properties": {
            "ticket_id": { "type": "string" }
        },
        "required": ["ticket_id"]
    }),
);
```

The pause kind is `external_output` when every pending call needs an external result. Supply each result by call ID:

```rust theme={null}
use phaseo_agent::{ContinueOptions, ToolOutput};

let outputs = paused.run.pause.as_ref().unwrap()
    .pending_tool_calls
    .iter()
    .map(|pending| ToolOutput {
        tool_call_id: pending.call.id.clone(),
        output: json!({
            "subject": "Provider latency increased",
            "priority": "high"
        }),
    })
    .collect();

let mut options = ContinueOptions::new(paused);
options.tool_outputs = outputs;

let completed = agent.continue_run(&mut client, options)?;
```

If one model turn mixes automatic and pending tools, the runtime executes the automatic tools before it returns the pause.

## Tool errors

An `AgentError` returned by a local executor becomes a structured tool error message and is sent back to the model. An unknown tool name or a missing approval/output fails continuation with `AgentError`.

## Related

* [Persist and resume runs](./agent-sdk-state-and-approval)
* [Agent API reference](./agent-sdk-api-reference)