Rate limits

X-RateLimit-Limit:     <window limit>
X-RateLimit-Remaining: <calls left>
X-RateLimit-Reset:     <unix epoch seconds when the window resets>

Retry-After: <seconds>

import { setTimeout as sleep } from 'node:timers/promises'

async function withRetry<T>(fn: () => Promise<Response>): Promise<T> {
  for (let attempt = 0; attempt < 5; attempt += 1) {
    const res = await fn()
    if (res.status !== 429) {
      if (!res.ok) throw new Error(`HTTP ${res.status}: ${await res.text()}`)
      return (await res.json()) as T
    }
    const retryAfterSec = Number(res.headers.get('Retry-After') ?? '1')
    const backoffSec = Math.max(retryAfterSec, 2 ** attempt)
    await sleep(backoffSec * 1000)
  }
  throw new Error('Exhausted retries after repeated 429 responses')
}

const sendResponse = await withRetry<{ status: string; runId: string }>(() =>
  fetch('https://brew.new/api/v1/sends', {
    method: 'POST',
    headers: {
      Authorization: `Bearer ${process.env.BREW_API_KEY!}`,
      'Content-Type': 'application/json',
      'Idempotency-Key': `send-promo-${Date.now()}`,
    },
    body: JSON.stringify({
      emailId: 'eml_abc',
      domainId: 'dom_brand_primary',
      audienceId: 'aud_subscribers',
      subject: 'Black Friday — 40% off',
    }),
  })
)

{
  "error": {
    "code": "RATE_LIMITED",
    "type": "rate_limit",
    "message": "Rate limit exceeded for emails.generate. Retry after 12s.",
    "suggestion": "Back off and retry after the duration in `Retry-After`.",
    "docs": "https://docs.brew.new/api-reference/api/rate-limits",
    "retryAfter": 12
  }
}