AVAILABLE FOR WEB, FLUTTER & QA PROJECTS
How to use this tool
1. Specify Expected Traffic
Enter daily or monthly active users and average API calls per session.
2. Choose Algorithm
Select Token Bucket, Leaky Bucket, Fixed Window Counter, or Sliding Window Log.
3. Set Rate Limit & Burst Capacity
Configure baseline requests per second (RPS) and burst multiplier for traffic spikes.
4. Review Redis Configuration
Copy ready-to-deploy rate-limiting parameters for Upstash Redis, Express, or Next.js middleware.
Formula or logic used
Rate Limiting & Token Bucket Algorithms
A token bucket refills at a constant rate $r$ tokens/second up to capacity $b$. Requests consume 1 token. Bursts up to capacity $b$ are permitted, while sustained loads are capped at $r$.
Average RPS = Total Daily Requests / (86,400 seconds × Concurrency Factor)Peak Burst RPS = Average RPS × Peak Multiplier (typically 3x to 5x)Bucket Capacity (b) = Peak Burst RPS × Allowed Burst Duration (seconds)Token Refill Rate (r) = Baseline Sustained RPSHTTP 429 Response Headers: Return `X-RateLimit-Limit`, `X-RateLimit-Remaining`, and `Retry-After`.
Examples
Example 1: Public SaaS REST API Tier
Absorbs short page load spikes while preventing automated denial-of-service abuse.
Example 2: AI Inference Microservice Rate Limit
Guarantees that inference worker queues never exceed GPU VRAM memory constraints.
Common use cases
Next.js API Route Throttling
Configure `@upstash/ratelimit` parameters in Next.js App Router middleware.
Microservice Database Protection
Cap incoming traffic at the maximum connection pool threshold of your PostgreSQL cluster.
Tiered SaaS Pricing Architecture
Design fair rate limits for Free (60 req/min), Pro (600 req/min), and Enterprise tiers.
DDoS & Scraping Mitigation
Throttle aggressive scrapers before they exhaust server CPU and network bandwidth.
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Frequently asked questions
What is the best rate limiting algorithm for web APIs?
The Token Bucket algorithm is generally the best for web applications because it allows legitimate short bursts (e.g. initial page loads requesting multiple endpoints) while maintaining a strict sustained rate limit.
What HTTP status code should rate limited requests return?
Always return HTTP 429 (Too Many Requests) accompanied by a `Retry-After` header indicating the number of seconds the client must wait before retrying.
How should rate limits be stored in a distributed system?
Use an in-memory datastore like Redis with atomic operations (Lua scripts or Redis cell) to ensure thread-safe rate limit tracking across multiple serverless or container instances.
What is the difference between Fixed Window and Sliding Window?
Fixed Window resets at a fixed clock boundary, which can allow double the allowed requests at the boundary edge. Sliding Window tracks a continuous time window, eliminating boundary burst spikes.
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