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

# tool-safety-classes

> Invoke classifies every tool call into one of four safety classes. The classification determines how Invoke routes the action and what controls apply.

Every tool registered with Invoke gets a safety class. The class tells Invoke how to handle the tool at runtime — what checks to run, whether to require approval, and how to reconcile unknown outcomes.

## The four safety classes

### Idempotent

Safe to call multiple times with the same result. No special handling is needed.

* **Examples:** `read_customer`, `list_invoices`, `get_deployment_status`
* **Behavior:** Invoke executes immediately with scope validation. No idempotency enforcement needed.

### Write-once-checkable

A single write that can be verified after the fact by querying live state.

* **Examples:** `stripe.charge_customer`, `create_linear_issue`, `send_email`
* **Behavior:** Invoke writes a commit record, then on retry checks live source-of-truth state before allowing another attempt. If the first write already succeeded, the retry is blocked.

### Irreversible

Cannot be undone once executed. Invoke applies strict identity and scope checks.

* **Examples:** `delete_account`, `cancel_subscription`, `purge_data`
* **Behavior:** Invoke enforces additional scope checks and identity validation. Mismatched state triggers `replan_required` instead of proceeding.

### Approval-bound

Requires a human decision before executing.

* **Examples:** `issue_refund`, `deploy_to_production`, `send_mass_notification`
* **Behavior:** Invoke stages the action and waits for approval. Before executing after approval, Invoke revalidates state to ensure conditions haven't changed since the approval was granted.

## How safety classes affect execution

| Safety Class         | Commit Record | Reconciliation | Approval Gate | State Revalidation |
| -------------------- | ------------- | -------------- | ------------- | ------------------ |
| Idempotent           | No            | No             | No            | No                 |
| Write-once-checkable | Yes           | Yes            | No            | No                 |
| Irreversible         | Yes           | Yes            | No            | Yes                |
| Approval-bound       | Yes           | Yes            | Yes           | Yes                |

## Configuring safety classes

You define safety classes in your Invoke project configuration when you register tools:

```json theme={null}
{
  "tools": {
    "stripe.charge_customer": {
      "safetyClass": "write-once-checkable",
      "idempotencyKey": "charge:{customer_id}:{amount}"
    },
    "delete_account": {
      "safetyClass": "irreversible"
    },
    "issue_refund": {
      "safetyClass": "approval-bound"
    }
  }
}
```

## Next steps

* [Reconciliation](/concepts/reconciliation) — how write-once-checkable tools handle unknown outcomes
* [Approvals](/concepts/approvals) — how approval-bound tools work end to end
* [Execution Records](/concepts/execution-records) — the durable record created for every non-idempotent call