X-WS-RateLimit-Limit

IONOS CDN applies per-IP rate limiting to incoming requests, and the X-WS-RateLimit-Limit unofficial response header reports which rate limit is configured for the routing rule that matched the request.

Note

The "X-" naming convention for HTTP headers, "X" referring to "experimental", has been deprecated and needs to be transitioned to the formal naming convention for HTTP headers.

Table of Contents

Standardized successor

The IETF is standardizing rate limit signaling under the RateLimit and RateLimit-Policy response fields, a vendor-neutral replacement for de facto rate limit headers like this one.

Usage

IONOS CDN rate limiting controls how many requests clients behind a single IP address are allowed to send each second. Administrators choose a rate limit class for each CDN routing rule, covering the scheme, hostname, and path prefix, and the X-WS-RateLimit-Limit header reports the configured ceiling back to the client.

Each edge server and each routing rule keeps its own bucket for the per-IP counters. Buckets are not shared across routes or edge servers, so the same client may see a different remaining budget depending on which edge server answers and which routing rule matches.

The header appears alongside X-WS-RateLimit-Remaining, which shows how many requests remain before the limit is reached. Together, these two headers give API clients a clear view of their current consumption relative to the allowed maximum.

This header follows the same pattern as the widely adopted X-RateLimit-Limit, but with the WS- prefix scoping the header to the IONOS CDN platform.

Values

Numeric request ceiling

The value is a positive integer representing the maximum requests permitted per second, per client IP, per routing rule. IONOS sets the ceiling through rate limit classes, currently documented from R1 (one request per second) up to R500 (500 requests per second).

Example

A response from an IONOS CDN edge server shows the rate limit ceiling. This value corresponds to the R500 class and means clients behind the requesting IP address are permitted 500 requests per second on the matched routing rule.

X-WS-RateLimit-Limit: 500

In practice, both rate limit headers appear together so API clients receive a complete picture of their current standing.

X-WS-RateLimit-Limit: 500
X-WS-RateLimit-Remaining: 493

See also

Last updated: August 11, 2026