Rate Limits & Compute Units

API Quotas, Compute Unit Costs, and Backoff Strategies

Tower enforces rate limits based on Compute Units (CU) consumed per minute and monthly quotas to ensure high availability and fair platform utilization.

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Plan Tiers & Quotas

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Compute Unit (CU) Costs by Endpoint

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Rate Limit Response Headers

Every HTTP response from Tower Developer APIs includes standard rate limit headers:

• X-RateLimit-Limit: Maximum requests permitted within the active 60-second rolling window.
• X-RateLimit-Remaining: Number of requests remaining in the current window.
• Retry-After: Seconds to wait before retrying when an HTTP 429 Too Many Requests is returned.

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Handling 429 Responses with Exponential Backoff

When your application hits rate limits (HTTP 429), implement exponential backoff with jitter to retry gracefully.

JavaScript / TypeScript

javascriptCopy
async function fetchWithRetry(url, options, maxRetries = 4, baseDelayMs = 500) {
  for (let attempt = 0; attempt < maxRetries; attempt++) {
    const response = await fetch(url, options);

    if (response.status !== 429) {
      return response;
    }

    const retryAfter = response.headers.get("Retry-After");
    const delay = retryAfter 
      ? parseInt(retryAfter, 10) * 1000 
      : baseDelayMs * Math.pow(2, attempt);

    console.warn(`Rate limit hit (429). Retrying in ${delay}ms...`);
    await new Promise((resolve) => setTimeout(resolve, delay));
  }

  throw new Error("Max retries exceeded for rate-limited endpoint.");
}

Python

pythonCopy
import time
import requests

def request_with_retry(method, url, headers=None, json=None, max_retries=4, base_delay=0.5):
    for attempt in range(max_retries):
        response = requests.request(method, url, headers=headers, json=json)
        
        if response.status_code != 429:
            return response
            
        retry_after = response.headers.get("Retry-After")
        delay = float(retry_after) if retry_after else base_delay * (2 ** attempt)
        
        print(f"Rate limit hit (429). Retrying in {delay}s...")
        time.sleep(delay)
        
    raise Exception("Max retries exceeded for rate-limited endpoint.")