# Credits and cost

Calls are paid in credits from your account balance. A fresh fetch costs; anything already held is free; a quote is exact; a budget is a hard stop.

## How a call is priced

-   **Fresh fetches cost credits.** Each platform page shows the starting price per op, live from the API. The price covers what was asked for; a listing that returns fewer rows than it could have is settled at what actually arrived.
-   **Anything already held is free.**A subject measured recently — within the op's freshness window — is served from what is held, for you and for everyone, at no charge. `provenance.source` says which happened.
-   **History never bills.** Every platform's `history` op reads the stored series of a subject already held.
-   **Failures are not charged.** A subject the source could not answer is refunded before the response is sent and named in `coverage`.

## Quote before you spend

Send the same call with `estimateOnly: true`. The response carries `data.creditsNeeded` and a per-item breakdown, spends nothing, and runs the very plan the real call would — so the number is exact, not indicative.

**Estimate**

```
{
  "request": { "op": "profiles", "subjects": ["example"] },
  "estimateOnly": true
}
```

## Hard budgets

`maxCredits` caps one call. When the cap cannot cover everything asked, the least valuable items are left out and each is named in `coverage.omitted` as `budget_exhausted`. You are never charged past the cap and never left guessing what was skipped.

Every response also carries `cost.creditsRemaining`, so a loop can stop itself without a balance call. When the balance cannot cover a call at all, the answer is `402` with `error.code = "insufficient_credits"` — see [Errors](https://zomler.com/docs/api/errors).

## Spending well

-   estimate\_only=true quotes the exact cost without spending
-   anything already held serves free — the second viewer never pays
-   one op per call; batch subjects inside the op
-   ops are independent — send several as parallel tool calls
-   a posts answer includes the author's profile; don't buy it twice
-   max\_credits caps a call; the least valuable items are omitted, named

Credits are bought and topped up in the dashboard under [Billing](https://app.zomler.com/payments). Spend per API key is listed under API keys, so what each integration costs is a line item, not a reconciliation.

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Source: https://zomler.com/docs/api/credits