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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.

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The four safety classes

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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.

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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.

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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.

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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.

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How safety classes affect execution

Safety ClassCommit RecordReconciliationApproval GateState Revalidation
IdempotentNoNoNoNo
Write-once-checkableYesYesNoNo
IrreversibleYesYesNoYes
Approval-boundYesYesYesYes

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Configuring safety classes

You define safety classes in your Invoke project configuration when you register tools: 
{
  "tools": {
    "stripe.charge_customer": {
      "safetyClass": "write-once-checkable",
      "idempotencyKey": "charge:{customer_id}:{amount}"
    },
    "delete_account": {
      "safetyClass": "irreversible"
    },
    "issue_refund": {
      "safetyClass": "approval-bound"
    }
  }
}

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Next steps

  • Reconciliation — how write-once-checkable tools handle unknown outcomes
  • Approvals — how approval-bound tools work end to end
  • Execution Records — the durable record created for every non-idempotent call