What is a rate limit simulator?

A rate limit simulator calculates how long a batch of API requests will take given a rate limit, concurrency level, and retry strategy. It helps you predict completion times, model retry overhead, and find the concurrency needed to hit a target deadline — all before writing any code.

How is effective throughput calculated?

Effective throughput is the minimum of your concurrency level and the API's requests-per-second rate. For example, with 100 requests/minute (1.67 rps) and 10 workers, throughput is min(10, 1.67) = 1.67 req/s — the rate limit is the bottleneck.

What is a dual rate limit (burst limit)?

Some APIs enforce two simultaneous limits: a sustained limit (e.g., 60 requests/minute) and a per-second burst cap (e.g., 3 requests/second). OpenAI's API works this way. Enable the burst limit toggle to model both constraints — the simulator applies whichever is stricter.

What does Max Retries do?

Max Retries caps how many times a single request can be retried after hitting the rate limit. With the cap set to 0 (unlimited), requests retry forever until they succeed. With a cap of 3, requests that still fail after 3 retry attempts are counted as permanently failed — visible in the Permanently Failed metric.

What does the Timeline tab show?

The Timeline chart plots cumulative completed requests over time. The solid line shows actual completion with rate limiting and retry overhead. The dashed line shows the ideal pace if there were no rate limit — only a concurrency cap. The shaded region marks the retry overhead phase.

How does the Reverse calculator work?

The Reverse calculator flips the question: instead of 'how long will this take?', it asks 'how many workers do I need to finish in X minutes?'. Enter your total requests, rate limit, and target time — it tells you the required concurrency and whether your target is achievable given the rate limit.

What is the difference between fixed and exponential backoff?

Fixed backoff waits the same number of seconds between each retry. Exponential backoff doubles the base delay with each attempt (e.g., 2s, 4s, 8s…). Exponential backoff is generally recommended for production systems as it reduces thundering herd problems during outages.

Are my inputs stored anywhere?

No. All calculations run entirely in your browser using JavaScript. No data is ever sent to any server.

Developer Tool

Simulate API Rate Limits
Instantly.

Calculate how long your batch jobs take under rate limiting. Model concurrency, retries, and backoff — all in the browser.

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Real-Time Results

Calculations update instantly as you type. See throughput and completion time without hitting submit.

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Retry Modeling

Simulate fixed and exponential backoff strategies with a custom base delay to see how retries affect total time.

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100% Private

Everything runs in your browser using pure JavaScript. No data is ever sent to any server.

Quick presets

⚙Configure

Total Requests

Sustained Rate Limit

Burst Limit (per second)dual-rate

Concurrency (workers)

Parallel workers making requests simultaneously

Retry Strategy

nonefixedexponential(recommended)

Retry Delay (seconds)

Base delay — doubles with each retry attempt

Max Retries per Request

0 = unlimited — requests retry forever until they succeed

Effective Throughput

1.67req/s

1.67 rps limit

Completion Time

52m

Base: 12m + Retry overhead: 40m

Violations

workers over limit

Retries

6.0K

+40m overhead

Your concurrency (10) exceeds the limit (1.67 rps). Reduce workers to ≤1 to eliminate violations.

Frequently Asked Questions

Everything you need to know about Rate Limit Simulator.

Simulate API Rate LimitsInstantly.

Real-Time Results

Retry Modeling

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Frequently Asked Questions

Simulate API Rate Limits
Instantly.