---
title: AI_InvalidToolApprovalSignatureError
description: Learn how to fix AI_InvalidToolApprovalSignatureError
---

# AI_InvalidToolApprovalSignatureError

This error occurs when `experimental_toolApprovalSecret` is configured and a tool approval replayed from the message history has a missing or invalid HMAC signature. The server rejects the approval before the tool executes.

Common causes:

- The approval was fabricated by the client (no signature present)
- The tool arguments were modified after the approval was signed
- The server secret changed between issuance and verification (e.g. after key rotation without overlap)

## Properties

- `approvalId`: The approval ID that failed verification
- `toolCallId`: The tool call ID the approval was for

## Checking for this Error

You can check if an error is an instance of `AI_InvalidToolApprovalSignatureError` using:

```typescript
import { InvalidToolApprovalSignatureError } from 'ai';

if (InvalidToolApprovalSignatureError.isInstance(error)) {
  // Handle the error
}
```