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

# Key limit

> Get notified immediately when an API key crosses a percentage of its limit

Key limit alerts you the moment a key's usage crosses a percentage of its period limit. Unlike [key exhaustion](/docs/alerts/key-exhaustion) — which forecasts ahead — key limit is reactive and fires as soon as the threshold is actually hit.

## When to use it

* You want to know the instant a key crosses, say, 80% or 90% of its cap.
* A safety net under [key exhaustion](/docs/alerts/key-exhaustion) — the forecast misses sometimes, the threshold doesn't.
* Keys with predictable, steady usage where a flat percentage is the most natural signal.

Keys without a period limit are skipped — there's nothing to measure against. Set a period limit on the key first.

## What you configure

| Setting                  | What it does                                                                 |
| ------------------------ | ---------------------------------------------------------------------------- |
| **Threshold Percentage** | Percentage of the period limit at which the alert fires (e.g. `80` for 80%). |

This is a reactive alert — no schedule, no scope picker. It evaluates each time the key is used.

## How you're notified

Email and/or SMS, based on your preferences in **Settings → Notifications**. A cooldown prevents repeat notifications while the key stays above the threshold. See [the alerts overview](/docs/alerts/overview) for delivery details.