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

# Limits and billing

> Rate limits and credits are both counted in scoring evaluations, not assets.

The single most important thing to internalize: **Kettio bills and rate-limits by scoring
evaluation, not by asset.** An agent that budgets by asset count will hit `429` earlier than it
expects.

## Rank API limits

| Limit                 | Value                                                 |
| --------------------- | ----------------------------------------------------- |
| Maximum assets        | 20 per request                                        |
| Concurrency           | Up to 4 assets evaluated at a time inside the request |
| Rate limit            | 60 scoring evaluations per minute per API key         |
| Close-pair refinement | At most 6 pairs per request                           |

## What an evaluation costs

| Asset shape                              | Evaluations                                  |
| ---------------------------------------- | -------------------------------------------- |
| Image only                               | 1                                            |
| With `copy_context` (ablation succeeded) | 2 — full ad package plus image-only ablation |
| With `copy_context` (ablation failed)    | 1                                            |
| Failed asset                             | 0 — failures are not billed                  |

Each evaluation contains three paired-model repetitions (six generator samples), but credits are
deducted per **successful scoring evaluation** — not per repetition and not per model call.

<Note>
  A 20-asset batch where every asset carries copy context can cost up to 40 evaluations. That is
  two thirds of your per-minute allowance in a single request.
</Note>

## Reading usage from the response

```json theme={null}
{
  "summary": {
    "assets_ranked": 1,
    "assets_failed": 0,
    "scoring_evaluations": 2,
    "repetitions_per_evaluation": 3,
    "generator_samples_per_evaluation": 6,
    "credits_used": 2,
    "credits_remaining": 48
  }
}
```

Track `scoring_evaluations` and `credits_remaining` rather than counting requests.

## Pairwise billing

The Pairwise API is accounted separately and reports `pairwise_evaluations` on its own.

| Result                     | Billed     |
| -------------------------- | ---------- |
| Completed five-voter panel | 1 credit   |
| `partial`                  | Not billed |
| `error`                    | Not billed |

Close-pair refinement inside the Rank API is reported under
`summary.close_pair_refinement`; Rank API credit and rate accounting is based on scoring
evaluations.

## Handling 429

`429` responses carry a `Retry-After` header. Honour it instead of retrying on a fixed
interval — there is a worked backoff implementation in the
[agent loop guide](/guides/agent-loop#rate-limit-backoff).

## Estimating before you send

```javascript theme={null}
function estimateEvaluations(assets) {
  return assets.reduce(
    (total, asset) => total + (asset.copy_context ? 2 : 1),
    0,
  );
}
```

This is an upper bound — failed assets and failed ablations both come in under it.