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

# Integrity Verification

> Verify cryptographic hash chain integrity for threads and steps

## Verify Hash Chain Integrity

<CodeGroup>
  ```graphql GraphQL theme={null}
  # Verify complete thread hash chain
  query {
    verifyThreadIntegrity(threadId: "thread-123") {
      verified
      totalEvents
      brokenAt
      error
    }
  }

  # Verify specific step
  query {
    verifyStepIntegrity(
      threadId: "thread-123"
      stepName: "order_placed"
      idempotencyKey: "order_456"
    ) {
      verified
      hash
      prevHash
    }
  }

  # Get hash chain data
  query {
    thread(id: "thread-123") {
      lastHash
      steps {
        stepName
        hash
        prevHash
        verified
      }
    }
  }
  ```
</CodeGroup>

## Hash Chain Status Fields

| Field            | Type     | Description                 |
| ---------------- | -------- | --------------------------- |
| `verified`       | Boolean! | Chain integrity verified    |
| `lastVerifiedAt` | String!  | Last verification timestamp |
| `totalEvents`    | Int!     | Total events in chain       |
| `brokenAt`       | String   | Timestamp where chain broke |
| `error`          | String   | Error message (if broken)   |

## Step Integrity Fields

| Field      | Type     | Description                |
| ---------- | -------- | -------------------------- |
| `verified` | Boolean! | Step integrity verified    |
| `hash`     | String   | Step hash                  |
| `prevHash` | String   | Previous step hash         |
| `error`    | String   | Error message (if invalid) |

## How Hash Chains Work

1. **First Step**: Hash = HMAC-SHA256(prevHash:threadID:stepID:stepName:idempotencyKey:timestamp)
2. **Subsequent Steps**: Each step's hash includes the previous step's hash
3. **Verification**: Recalculate hashes and compare with stored values
4. **Tamper Detection**: Any modification breaks the chain

## Use Cases

| Use Case              | Description                                        |
| --------------------- | -------------------------------------------------- |
| **Audit Trail**       | Verify execution history hasn't been tampered with |
| **Detect Tampering**  | Identify where integrity was compromised           |
| **Step Verification** | Verify individual step integrity                   |
| **Compliance**        | Prove execution order for regulatory requirements  |

## Next Steps

<CardGroup cols={2}>
  <Card title="Step Queries" icon="list" href="/api-reference/step-queries">
    Query step execution history
  </Card>

  <Card title="Thread Queries" icon="database" href="/api-reference/thread-queries">
    Query thread data
  </Card>
</CardGroup>