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

# Signed Receipts

> Every request emits an ED25519-signed, hash-chained receipt — tamper-evident audit evidence for compliance.

Every request through the gateway produces a **receipt**: a canonical record of what happened — who called, which model, what it cost, and which policy checks ran — cryptographically signed and chained to the receipt before it. The result is an audit trail where tampering with any single record is detectable.

Observability tools can tell you what they *observed*. Because Wardin sits in the request path and signs what it *enforced*, a receipt is evidence, not telemetry.

## What a receipt contains

| Field                                 | Description                                                                              |
| ------------------------------------- | ---------------------------------------------------------------------------------------- |
| `request_id`                          | Unique ID of the request                                                                 |
| `tenant_id`                           | Your organization                                                                        |
| `actor`                               | The user/key the request is attributed to                                                |
| `provider` / `model`                  | Who served it and with what                                                              |
| `prompt_tokens` / `completion_tokens` | Token usage                                                                              |
| `cost_usd`                            | Actual cost committed for the request                                                    |
| `checks`                              | Ordered list of policy decisions (`{name, result}`) — budget, allowlist, guardrails, PII |
| `ts`                                  | Timestamp (RFC 3339, UTC, millisecond precision)                                         |

## How the chain works

1. The receipt's fields are serialized in a fixed canonical order.
2. `this_hash = sha256(canonical_receipt || prev_hash)` — each receipt's hash incorporates the previous receipt's hash.
3. `this_hash` is signed with the gateway's **ED25519** key.

Changing any field of any historical receipt changes its hash, which breaks every subsequent link in the chain. Verification re-derives the hashes from stored fields and checks the signature — nothing is taken on trust.

<Note>
  Chaining and signing happen in an asynchronous writer, off the response path. Receipts
  add **zero latency** to your LLM requests, and the chain only advances after the
  receipt is durably stored.
</Note>

## Where to see receipts

* **INGRESS** — click any request in the live stream to open its receipt drawer (with `RECEIPT | TRACE` tabs).
* **EVIDENCE** — chain statistics, a sample verified receipt, and the compliance-framework view.

## Verifying programmatically

```bash theme={null}
# List recent receipts (newest first, cursor pagination)
curl "https://api.wardin.ai/v1/receipts?limit=25" \
  -H "Authorization: Bearer wardin_sk_ADMIN_KEY"

# Fetch one receipt and verify its hash + ED25519 signature
curl "https://api.wardin.ai/v1/receipts/RECEIPT_UUID" \
  -H "Authorization: Bearer wardin_sk_ADMIN_KEY"
# → { ..., "verified": true }

# Verify a contiguous range of the chain — reports the first broken link, if any
curl "https://api.wardin.ai/v1/receipts/_/verify-chain?from=1&to=100" \
  -H "Authorization: Bearer wardin_sk_ADMIN_KEY"
```

`verified: true` means the stored hash equals `sha256(canonical || prev_hash)` **and** the ED25519 signature over that hash is valid. Receipts are tenant-scoped — you can only read your own.

## Why this matters for compliance

Frameworks like the **EU AI Act** and **NIST AI RMF** ask for evidence that governance controls actually ran — not a dashboard screenshot. A hash-chained, signed record of every enforcement decision (including blocks: over-budget 429s, allowlist 403s, guardrail rejections) is exactly that artifact, exportable and independently verifiable.