Concurrency refers to the number of ongoing requests that happen at any given time. By different means, computers and languages can call the API in parallel and wait for results while others are still running. You can use concurrency with any ZenRows plan; check out pricing for more details.

For more details, check our how-to guide on concurrency to see details about implementation in Python and JavaScript.

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How many concurrent requests are included in my plan?

The concurrency limit varies by subscription plan:

  • Trial plan: 5 concurrent requests
  • Developer plan: 20 concurrent requests
  • Startup plan: 50 concurrent requests
  • Business plan: 100 concurrent requests
  • Business 500: 150 concurrent requests
  • Business 1K: 200 concurrent requests
  • Business 2K: 300 concurrent requests
  • Business 3K: 400 concurrent requests

Enterprise plans can include custom concurrency limits to fit your needs. Contact us for tailor-made Enterprise solutions.

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If get a “429 Too Many Requests” error, do I lose that request or is it queued?

You’ll receive an error, and that request won’t be queued or retried automatically. You’ll need to manage retries on your end, ensuring you don’t exceed your concurrency limit.

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Can I increase my concurrency limit?

Absolutely! We offer various plans with different concurrency limits to suit your needs. If you find yourself frequently hitting the concurrency limit, consider upgrading.

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How can I monitor my concurrency usage?

When using the Universal Scraper API, each response includes these helpful headers:

  • Concurrency-Limit: Shows your maximum concurrent request limit
  • Concurrency-Remaining: Shows how many free concurrency slots you have available

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I’ve been blocked by repeatedly exceeding my concurrency limit. Why?

Whenever you exceed your plan concurrency limit, you’ll start receiving “429 Too Many Requests” errors. If you keep sending more and more requests exceeding your plan concurrency limit in a short period of time, the service may temporarily block your IP address to prevent API misuse.

The IP address ban will last only a few minutes, but repeatedly being blocked might end in a long-lasting block. Check the concurrency optimization section for more information on how to limit concurrent requests to prevent being blocked.

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