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Fast and efficient in-memory rate-limit for Node, used to alleviate DOS attacks.





Fast and efficient in-memory rate-limit, used to alleviate most common DOS attacks.

Based on, but updated to work with modern Node versions. This module uses the ES Map instead of the native hashtable package.


npm install --save @kidkarolis/not-so-fast

How to use?

The not-so-fast API is pretty simple, here are some keywords used in the docs:

  • ratelimiter: ratelimiter instance, which plays the role of limits storage
  • namespace: the master ratelimit storage namespace (eg: set namespace to the user client IP, or user username)

You can create as many ratelimiter instances as you need in your application. This is great if you need to rate-limit IPs on specific zones (eg: for a chat application, you don't want the message send rate limit to affect the message composing notification rate limit).

Here's how to proceed (we take the example of rate-limiting messages sending in a chat app):

1. Create the rate-limiter

The rate-limiter can be instanciated as such:

const RateLimiter = require("@kidkarolis/not-so-fast");

const messageLimiter = new RateLimiter({
  threshold : 20, // available tokens over timespan
  ttl       : 60  // time-to-live value of token bucket (in seconds)

This limiter will allow 20 messages to be sent every minute per namespace. An user can send a maximum number of 20 messages in a 1 minute timespan, with a token counter reset every minute for a given namespace.

The reset scheduling is done per-namespace; eg: if namespace user_1 sends 1 message at 11:00:32am, he will have 19 messages remaining from 11:00:32am to 11:01:32am. Hence, his limiter will reset at 11:01:32am, and won't scheduler any more reset until he consumes another token.

2. Check by consuming a token

On the message send portion of our application code, we would add a call to the ratelimiter instance.

2.1. Consume token with asynchronous API (Promise catch/reject)

// This would be dynamic in your application, based on user session data, or user IP
namespace = "user_1";

// Check if user is allowed to send message
  .then(() => {
    // Consumed a token
    // Send message
  .catch(() => {
    // No more token for namespace in current timespan
    // Silently discard message

2.2. Consume token with synchronous API (boolean test)

// This would be dynamic in your application, based on user session data, or user IP
namespace = "user_1";

// Check if user is allowed to send message
if (messageLimiter.consumeSync(namespace) === true) {
  // Consumed a token
  // Send message
} else {
  // consumeSync returned false since there is no more tokens available
  // Silently discard message

3. Check without consuming a token

In some instances, like password brute forcing prevention, you may want to check without consuming a token and consume only when password validation fails.

3.1. Check whether there are remaining tokens with asynchronous API (Promise catch/reject)

limiter.hasToken(request.ip).then(() => {
  return authenticate(request.login, request.password)
    () => {
      // User is authenticated

    () => {
      // User is not authenticated
      // Consume a token and reject promise
      return limiter.consume(request.ip)
        .then(() => Promise.reject())
  .catch(() => {
    // Either invalid authentication or too many invalid login
    return response.unauthorized();

3.2. Check whether there are remaining tokens with synchronous API (boolean test)

if (!limiter.hasTokensSync(request.ip)) {
  throw new Error("Too many invalid login");

const isAuthenticated = authenticateSync(request.login, request.password);

if (!isAuthenticated) {

  throw new Error("Invalid login/password");