Express Rate Limit

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Basic rate-limiting middleware for Express. Use to limit repeated requests to public APIs and/or endpoints such as password reset. Plays nice with express-slow-down.

Use Cases

Depending on your use case, you may want to switch to a different store.

Abuse Prevention

The default MemoryStore is probably fine.

API Rate Limit Enforcement

The default MemoryStore stores the hit counts for clients in memory, and is thus unsuitable for use when running multiple servers or processes.

If you have multiple processes on a single server (via the node:cluster module), the cluster-memory-store will keep them all in sync without needing an external data store.

If you have multiple servers, or want to maintain state across app restarts, use an external data store such as redis, memcached, etc..

Alternate Rate Limiters

This module was designed to only handle the basics and didn't even support external stores initially. These other options all are excellent pieces of software and may be more appropriate for some situations:

• rate-limiter-flexible
• express-brute
• rate-limiter

Installation

From the npm registry:

# Using npm
> npm install express-rate-limit
# Using yarn or pnpm
> yarn/pnpm add express-rate-limit

From Github Releases:

# Using npm
> npm install https://github.com/express-rate-limit/express-rate-limit/releases/download/v{version}/express-rate-limit.tgz
# Using yarn or pnpm
> yarn/pnpm add https://github.com/express-rate-limit/express-rate-limit/releases/download/v{version}/express-rate-limit.tgz

Replace {version} with the version of the package that you want to your, e.g.: 6.0.0.

Usage

Importing

This library is provided in ESM as well as CJS forms, and works with both Javascript and Typescript projects.

This package requires you to use Node 16 or above.

Import it in a CommonJS project (type: commonjs or no type field in package.json) as follows:

const { rateLimit } = require('express-rate-limit')

Import it in a ESM project (type: module in package.json) as follows:

import { rateLimit } from 'express-rate-limit'

Examples

To use it in an API-only server where the rate-limiter should be applied to all requests:

import { rateLimit } from 'express-rate-limit'

const limiter = rateLimit({
	windowMs: 15 * 60 * 1000, // 15 minutes
	limit: 100, // Limit each IP to 100 requests per `window` (here, per 15 minutes)
	standardHeaders: 'draft-7', // draft-6: `RateLimit-*` headers; draft-7: combined `RateLimit` header
	legacyHeaders: false, // Disable the `X-RateLimit-*` headers
	// store: ... , // Use an external store for more precise rate limiting
})

// Apply the rate limiting middleware to all requests
app.use(limiter)

To use it in a 'regular' web server (e.g. anything that uses express.static()), where the rate-limiter should only apply to certain requests:

import { rateLimit } from 'express-rate-limit'

const apiLimiter = rateLimit({
	windowMs: 15 * 60 * 1000, // 15 minutes
	limit: 100, // Limit each IP to 100 requests per `window` (here, per 15 minutes)
	standardHeaders: 'draft-7', // Set `RateLimit` and `RateLimit-Policy` headers
	legacyHeaders: false, // Disable the `X-RateLimit-*` headers
	// store: ... , // Use an external store for more precise rate limiting
})

// Apply the rate limiting middleware to API calls only
app.use('/api', apiLimiter)

To create multiple instances to apply different rules to different endpoints:

import { rateLimit } from 'express-rate-limit'

const apiLimiter = rateLimit({
	windowMs: 15 * 60 * 1000, // 15 minutes
	limit: 100, // Limit each IP to 100 requests per `window` (here, per 15 minutes)
	standardHeaders: 'draft-7', // draft-6: `RateLimit-*` headers; draft-7: combined `RateLimit` header
	legacyHeaders: false, // Disable the `X-RateLimit-*` headers
	// store: ... , // Use an external store for more precise rate limiting
})

app.use('/api/', apiLimiter)

const createAccountLimiter = rateLimit({
	windowMs: 60 * 60 * 1000, // 1 hour
	limit: 5, // Limit each IP to 5 create account requests per `window` (here, per hour)
	message:
		'Too many accounts created from this IP, please try again after an hour',
	standardHeaders: 'draft-7', // draft-6: `RateLimit-*` headers; draft-7: combined `RateLimit` header
	legacyHeaders: false, // Disable the `X-RateLimit-*` headers
})

app.post('/create-account', createAccountLimiter, (req, res) => {
	//...
})

To use a custom store:

import { rateLimit } from 'express-rate-limit'
import RedisStore from 'rate-limit-redis'
import RedisClient from 'ioredis'

const redisClient = new RedisClient()
const rateLimiter = rateLimit({
	windowMs: 15 * 60 * 1000, // 15 minutes
	limit: 100, // Limit each IP to 100 requests per `window` (here, per 15 minutes)
	standardHeaders: 'draft-7', // draft-6: `RateLimit-*` headers; draft-7: combined `RateLimit` header
	legacyHeaders: false, // Disable the `X-RateLimit-*` headers
	store: new RedisStore({
		/* ... */
	}), // Use the external store
})

// Apply the rate limiting middleware to all requests
app.use(rateLimiter)

Note: most stores will require additional configuration, such as custom prefixes, when using multiple instances. The default built-in memory store is an exception to this rule.

Troubleshooting Proxy Issues

Please take a look at the wiki page on this issue.

Configuration

windowMs

number

Time frame for which requests are checked/remembered. Also used in the Retry-After header when the limit is reached.

Note: with stores that do not implement the init function (see the table in the stores section below), you may need to configure this value twice, once here and once on the store. In some cases the units also differ (e.g. seconds vs miliseconds).

Defaults to 60000 ms (= 1 minute).

limit

number | function

The maximum number of connections to allow during the window before rate limiting the client.

Can be the limit itself as a number or a (sync/async) function that accepts the Express req and res objects and then returns a number.

Set it to 0 to disable the rate limiter. As of version 7.0.0, setting max to zero will no longer disable the rate limiter - instead, it will 'block' all requests to that endpoint.

Defaults to 5.

Renamed in v7.x from max to limit. However, max will still be supported for backwards-compatibility.

An example of using a function:

const isPremium = async (user) => {
	// ...
}

const limiter = rateLimit({
	// ...
	limit: async (req, res) => {
		if (await isPremium(req.user)) return 10
		else return 5
	},
})

message

any

The response body to send back when a client is rate limited.

May be a string, JSON object, or any other value that Express's res.send method supports. It can also be a (sync/async) function that accepts the Express request and response objects and then returns a string, JSON object or any other value the Express res.send function accepts.

Defaults to 'Too many requests, please try again later.'

An example of using a function:

const isPremium = async (user) => {
	// ...
}

const limiter = rateLimit({
	// ...
	message: async (req, res) => {
		if (await isPremium(req.user))
			return 'You can only make 10 requests every hour.'
		else return 'You can only make 5 requests every hour.'
	},
})

statusCode

number

The HTTP status code to send back when a client is rate limited.

Defaults to 429 (HTTP 429 Too Many Requests - RFC 6585).

legacyHeaders

boolean

Whether to send the legacy rate limit headers for the limit (X-RateLimit-Limit), current usage (X-RateLimit-Remaining) and reset time (if the store provides it) (X-RateLimit-Reset) on all responses. If set to true, the middleware also sends the Retry-After header on all blocked requests.

Defaults to true (for backward compatibility).

Renamed in 6.x from headers to legacyHeaders.

standardHeaders

boolean | 'draft-6' | 'draft-7'

Whether to enable support for headers conforming to the RateLimit header fields for HTTP standardization draft adopted by the IETF.

If set to draft-6, separate RateLimit-Policy RateLimit-Limit, RateLimit-Remaining, and, if the store supports it, RateLimit-Reset headers are set on the response, in accordance with draft-ietf-httpapi-ratelimit-headers-06.

If set to draft-7, a combined RateLimit header is set containing limit, remaining, and reset values, and a RateLimit-Policy header is set, in accordiance with draft-ietf-httpapi-ratelimit-headers-07. windowMs is used for the reset value if the store does not provide a reset time.

If set to true, it is treated as draft-6, however this behavior may change in a future semver major release.

If set to any truthy value, the middleware also sends the Retry-After header on all blocked requests.

The standardHeaders option may be used in conjunction with, or instead of the legacyHeaders option.

ℹ️ Tip: use ratelimit-header-parser in clients to read/parse any form of express-rate-limit's headers.

Defaults to false.

Renamed in 6.x from draft_polli_ratelimit_headers to standardHeaders.

requestPropertyName

string

The name of the property on the Express request object to store the rate limit info.

Defaults to 'rateLimit'.

skipFailedRequests

boolean

When set to true, failed requests won't be counted. Request considered failed when the requestWasSuccessful option returns false. By default, this means requests fail when:

• the response status >= 400
• the request was cancelled before last chunk of data was sent (response close event triggered)
• the response error event was triggered by response

(Technically they are counted and then un-counted, so a large number of slow requests all at once could still trigger a rate-limit. This may be fixed in a future release. PRs welcome!)

Defaults to false.

skipSuccessfulRequests

boolean

If true, the library will (by default) skip all requests that are considered 'failed' by the requestWasSuccessful function. By default, this means requests succeed when the response status code < 400.

(Technically they are counted and then un-counted, so a large number of slow requests all at once could still trigger a rate-limit. This may be fixed in a future release. PRs welcome!)

Defaults to false.

keyGenerator

function

Method to retrieve custom identifiers for clients, such as their IP address, username, or API Key.

Should be a (sync/async) function that accepts the Express request and response objects and then returns a string.

By default, the client's IP address is used:

const limiter = rateLimit({
	// ...
	keyGenerator: (req, res) => req.ip,
})

Note If a keyGenerator returns the same value for every user, it becomes a global rate limiter. This could be combined with a second instance of express-rate-limit to have both global and per-user limits.

handler

function

Express request handler that sends back a response when a client is rate-limited.

By default, sends back the statusCode and message set via the options, similar to this:

const limiter = rateLimit({
	// ...
	handler: (req, res, next, options) =>
		res.status(options.statusCode).send(options.message),
})

skip

function

Function to determine whether or not this request counts towards a client's quota. Should be a (sync/async) function that accepts the Express request and response objects and then returns true or false.

Could also act as an allowlist for certain keys:

const allowlist = ['192.168.0.56', '192.168.0.21']

const limiter = rateLimit({
	// ...
	skip: (req, res) => allowlist.includes(req.ip),
})

By default, it skips no requests:

const limiter = rateLimit({
	// ...
	skip: (req, res) => false,
})

requestWasSuccessful

function

Method to determine whether or not the request counts as 'succesful'. Used when either skipSuccessfulRequests or skipFailedRequests is set to true. Should be a (sync/async) function that accepts the Express req and res objects and then returns true or false.

By default, requests with a response status code less than 400 are considered successful:

const limiter = rateLimit({
	// ...
	requestWasSuccessful: (req, res) => res.statusCode < 400,
})

validate

boolean | Object

When enabled, a set of validation checks are run at creation and on the first request to detect common misconfigurations with proxies, etc. Prints an error to the console if any issue is detected.

Automatically disables after the first request is processed.

If set to true or false, all validations are enabled or disabled.

If set to an object, individual validations can be enabled or disabled by name, and the key default controls all unspecified validations. For example:

const limiter = rateLimit({
	validate: {
		xForwardedForHeader: false,
		default: true,
	},
	// ...
})

Supported options are ip, trustProxy, xForwardedForHeader, positiveHits, singleCount, limit, draftPolliHeaders, onLimitReached, headersResetTime, validationsConfig, and default.

See https://github.com/express-rate-limit/express-rate-limit/wiki/Error-Codes for more info.

Defaults to true.

store

Store

The Store to use to store the hit count for each client.

By default, the memory-store is used.

Here is a list of external stores:

Name	Description	Legacy/Modern
memory-store	(default) Simple in-memory option. Does not share state when app has multiple processes or servers.	Modern as of v6.0.0
cluster-memory-store	A memory-store wrapper that shares state across all processes on a server via the node:cluster module.	Modern
rate-limit-redis	A Redis-backed store, more suitable for large or demanding deployments.	Modern as of v3.0.0
rate-limit-memcached	A Memcached-backed store.	Modern as of v1.0.0
rate-limit-mongo	A MongoDB-backed store.	Legacy
precise-memory-rate-limit	A memory store similar to the built-in one, except that it stores a distinct timestamp for each key.	Modern as of v2.0.0
rate-limit-postgresql	A PostgreSQL-backed store.	Modern as of v1.1.0

Take a look at this guide if you wish to create your own store.

Request API

A req.rateLimit property is added to all requests with the limit, used, and remaining number of requests and, if the store provides it, a resetTime Date object. These may be used in your application code to take additional actions or inform the user of their status.

Note that used includes the current request, so it should always be > 0.

The property name can be configured with the configuration option requestPropertyName.

Instance API

resetKey(key)

Resets the rate limiting for a given key. An example use case is to allow users to complete a captcha to reset their rate limit, then call this function.

getKey(key)

Retrieves the hit count and reset time from the store for a given key.

Issues and Contributing

If you encounter a bug or want to see something added/changed, please go ahead and open an issue! If you need help with something, feel free to start a discussion!

If you wish to contribute to the library, thanks! First, please read the contributing guide. Then you can pick up any issue and fix/implement it!

License

MIT © Nathan Friedly, Vedant K