Developer documentation

Limits are counted per API key over a rolling minute. Every key of your account has its own budget, so one busy integration does not slow down another.

One send request can carry up to 10,000 recipients, so the send limit caps request count, not SMS volume.

On send endpoints, the X-RateLimit-* headers report the general 120 per minute budget; sends are additionally capped at 30 per minute per key. When the send cap trips, the 429's data.limit and Retry-After describe the send limit.

Headers

• X-RateLimit-Limit: the general per-key limit of 120 requests per minute.
• X-RateLimit-Remaining: requests left in the current window.
• Retry-After: on a 429, the seconds to wait before retrying.

When you hit the limit

The API returns 429 rate_limited. data.limit is the limit you hit (the send limit when a send trips it) and data.retry_after is the number of seconds to wait.

{
    "success": false,
    "message": "Too many requests, retry after 12 seconds",
    "data": { "limit": 30, "retry_after": 12 },
    "errors": { "rate_limit": ["Too many requests, retry after 12 seconds"] },
    "code": 429,
    "error_code": "rate_limited",
    "timestamp": "2026-09-26T10:00:00.000000Z"
}

Backing off

• Wait at least retry_after seconds, then retry with the same Idempotency-Key.
• For repeated 429s, back off exponentially with jitter (for example 1, 2, 4, 8 seconds plus a random fraction).
• Batch recipients into one broadcast or send-many request instead of sending one request per number.
• Watch X-RateLimit-Remaining and slow down before it reaches zero.