---
title: ratelimit.check_rates
summary: null
url: >-
  https://www.fastly.com/documentation/reference/vcl/functions/rate-limiting/ratelimit-check-rates
---

```
BOOL ratelimit.check_rates(STRING entry, ID rc1, INTEGER delta1, INTEGER window1, INTEGER limit1, ID rc2, INTEGER delta2, INTEGER window2, INTEGER limit2, ID pb, TIME ttl)
```

**Available in:** all subroutines

Increment the same entry in _two_ distinct ratecounters, each with different
windowing and limit parameters, as well as check if the client has exceeded some average
number of requests per second (RPS) for either ratecounter.

The lowest rate limit supported by this feature to demonstrate effective
behavior is 10 RPS. Using a limit below 10 RPS may result in unpredictable
accuracy and detection time.

## Parameters

`entry` - The entry to keep track of. Typically `client.ip` and any associated
metadata. An entry can be, at maximum, 256 bytes long.

`rc1` - The first ratecounter that tracks requests. When a user makes a
request, a ratecounter tracks that users average rate of requests over time.

`delta1` - The integer value to increment the entry in the rate counter by.
Typically, a value of 1 is used. The value must be between 0 and 100000.

`window1` - The last N seconds of data to compute the requests-per-second over.
Must be 1, 10, or 60.

`limit1` - The RPS limit. If the user goes above this limit, over the given
window, then they are penalized and their entry is put into the penalty box
`pb`. Must be between 10 and 70000000.

`rc2` - The second ratecounter that tracks requests.

`delta2` - The integer value to increment the entry in the rate counter by.
Typically, a value of 1 is used. The value must be between 0 and 100000.

`window2` - The last N seconds of data to compute the requests-per-second over.
Must be 1, 10, or 60.

`limit2` - The RPS limit. If the user goes above this limit, over the given
window, then they are penalized and their entry is put into the penalty box
`pb`. Must be between 10 and 70000000.

`pb` - The penalty box. Keeps track of penalized users. If a user is penalized,
their entry is put into this penalty box.

`ttl` - The penalty box TTL. Specifies how long a user remains penalized. Must
be between 1m and 1h, and has minute granularity (rounded to the nearest
minute).

## Return value

Upon completion, this function returns `true` if the user is penalized (i.e.
should be rate limited), or `false` if not.

In the event an error occurs, the default return value is `false`; therefore
errors (via `fastly.error`) must be handled specifically.

## Errors

If the given `entry` is longer than 256 bytes, then `false` is returned, and
`fastly.error` is set to `EINVAL`.

## Example

The following example will immediately halt and return a 429 to the client if
they exceed a rate of 1000 requests per second over the last 60 seconds, OR a
rate of 150 requests over the last 1 second.  The user will be penalized for 20
minutes afterword:

```vcl
penaltybox pbox { }
ratecounter rc1 { }
ratecounter rc2 { }

sub vcl_recv {
  if (ratelimit.check_rates(client.ip, rc1, 1, 60, 1000, rc2, 1, 1, 150, pbox, 20m)) {
    error 429 "Too many requests";
  }
}
```