express-rate-limit

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 need to switch to a different store.

Abuse Prevention

The default MemoryStore is probably fine.

API Rate Limit Enforcement

You likely want to switch to a different store. As a performance optimization, the default MemoryStore uses a global time window, so if your limit is 10 requests per minute, a single user might be able to get an initial burst of up to 20 requests in a row if they happen to get the first 10 in at the end of one minute and the next 10 in at the start of the next minute. (After the initial burst, they will be limited to the expected 10 requests per minute.) All other stores use per-user time windows, so a user will get exactly 10 requests regardless.

Additionally, if you have multiple servers or processes (for example, with the node:cluster module), you'll likely want to use an external data store to syhcnronize hits (redis, memcached, etc.) This will guarentee the expected result even if some requests get handled by different servers/processes.

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 14 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
	max: 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, // 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
	max: 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
	max: 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, // 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
	max: 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, // X-RateLimit-* headers
})

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

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
	max: 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, // 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

If you are behind a proxy/load balancer (usually the case with most hosting services, e.g. Heroku, Bluemix, AWS ELB, Nginx, Cloudflare, Akamai, Fastly, Firebase Hosting, Rackspace LB, Riverbed Stingray, etc.), the IP address of the request might be the IP of the load balancer/reverse proxy (making the rate limiter effectively a global one and blocking all requests once the limit is reached) or undefined. To solve this issue, add the following line to your code (right after you create the express application):

app.set('trust proxy', numberOfProxies)

Where numberOfProxies is the number of proxies between the user and the server. To find the correct number, create a test endpoint that returns the client IP:

app.set('trust proxy', 1)
app.get('/ip', (request, response) => response.send(request.ip))

Go to /ip and see the IP address returned in the response. If it matches your public IP address, then the number of proxies is correct and the rate limiter should now work correctly. If not, then keep increasing the number until it does.

For more information about the trust proxy setting, take a look at the official Express documentation.

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).

max

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 request and response objects and then returns a number.

Defaults to 5. Set it to 0 to disable the rate limiter.

An example of using a function:

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

const limiter = rateLimit({
	// ...
	max: async (request, response) => {
		if (await isPremium(request.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 response.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 response.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 (request, response) => {
		if (await isPremium(request.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: (request, response) => request.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: (request, response, next, options) =>
		response.status(options.statusCode).send(options.message),
})

onLimitReached

function

A (sync/async) function that accepts the Express request and response objects that is called the on the request where a client has just exceeded their rate limit.

This method was deprecated in v6 - Please use a custom handler that checks the number of hits instead.

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: (request, response) => allowlist.includes(request.ip),
})

By default, it skips no requests:

const limiter = rateLimit({
	// ...
	skip: (request, response) => 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 request and response 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: (request, response) => response.statusCode < 400,
})

validate

boolean

When enabled, a set of validation checks are run 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.

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
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.	Legacy
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

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

Request API

A request.rateLimit property is added to all requests with the limit, current, 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.

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 or whatever to reset their rate limit, then call this method.

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