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

# Spend limit policy

> Cap a session key's cumulative token spend over a rolling period - enforced on-chain in __check_auth.

`spendLimit` caps how much of a given token a session key may spend over a rolling time
window. The limit is enforced **on-chain** in the contract's `__check_auth` - not in the
SDK, not in the facilitator. A stolen session blob still cannot exceed its configured cap.

## Usage

```ts theme={null}
import { spendLimit } from "@buckspay/accounts/policy";

const policy = spendLimit({
  token: USDC_SAC,    // C-address of the token to cap
  max: "100",         // maximum spend in display units (e.g. "100" = 100 USDC)
  period: "day"       // rolling window: "day" | "week" | "month" | "total"
});
```

Pass the policy in the `policies` array when calling `grantSession`:

```ts theme={null}
const { session } = await client.grantSession({
  sessionKey: { type: "ed25519", publicKey: sessionKp.publicKey() },
  policies: [spendLimit({ token: USDC_SAC, max: "100", period: "day" })],
  expiresAt: Date.now() + 86_400_000
});
```

## Period values

| Value     | Window                                  |
| --------- | --------------------------------------- |
| `"day"`   | Rolling 24-hour window                  |
| `"week"`  | Rolling 7-day window                    |
| `"month"` | Rolling 30-day window                   |
| `"total"` | Lifetime cap for the session (no reset) |

## What happens when the limit is exceeded

A payment that would exceed the cap is rejected by the contract during `__check_auth`. The
facilitator maps the on-chain rejection to `BuckspayError("SESSION_POLICY_VIOLATION")`.

<Note>
  The limit is per-session, per-token. Two separate sessions each with `max: "100"` can each
  spend up to 100 USDC independently.
</Note>

## Combining policies

`spendLimit` is commonly paired with `allowlist` so the session key is scoped both by
spend and by callable contracts. See [Sessions overview](/features/sessions/overview) for
the full lifecycle example.

## Next

<CardGroup cols={2}>
  <Card title="Allowlist policy" href="/features/sessions/allowlist">
    Restrict which contracts the session key may call.
  </Card>

  <Card title="Sessions overview" href="/features/sessions/overview">
    Full lifecycle: grant, serialize, use, and revoke a session.
  </Card>
</CardGroup>