Node.js rate limiting reference
Arcjet rate limiting allows you to define rules which limit the number of requests a client can make over a period of time.
Configuration options
Each rate limit is configured on an exact path with a set of client characteristics and algorithm specific options.
Fixed window rate limit options
Tracks the number of requests made by a client over a fixed time window. Options are explained in the Configuration documentation. See the fixed window algorithm description for more details about how the algorithm works.
// Options for fixed window rate limit// See https://docs.arcjet.com/rate-limiting/configurationtype FixedWindowRateLimitOptions = { mode?: "LIVE" | "DRY_RUN"; // "LIVE" will block requests. "DRY_RUN" will log only match?: string; // request path the rate limit applies to characteristics?: string[]; // how the client is identified. Defaults to the global characteristics if unset window: string; // time window the rate limit applies to max: number; // maximum number of requests allowed in the time window};
Fixed window example
import arcjet, { fixedWindow } from "@arcjet/node";
const aj = arcjet({ key: process.env.ARCJET_KEY, characteristics: ["ip.src"], // track requests by IP address rules: [ fixedWindow({ mode: "LIVE", // will block requests. Use "DRY_RUN" to log only match: "/api/hello", // match all requests to /api/hello window: "60s", // 60 second fixed window max: 100, // allow a maximum of 100 requests }), ],});
Sliding window rate limit options
Tracks the number of requests made by a client over a sliding window so that the window moves with time. Options are explained in the Configuration documentation. See the sliding window algorithm description for more details about how the algorithm works.
// Options for sliding window rate limit// See https://docs.arcjet.com/rate-limiting/configurationtype SlidingWindowRateLimitOptions = { mode?: "LIVE" | "DRY_RUN"; // "LIVE" will block requests. "DRY_RUN" will log only match?: string; // request path the rate limit applies to characteristics?: string[]; // how the client is identified. Defaults to the global characteristics if unset interval: number; // the time interval in seconds for the rate limit max: number; // maximum number of requests allowed over the time interval};
Sliding window example
import arcjet, { slidingWindow } from "@arcjet/node";
const aj = arcjet({ key: process.env.ARCJET_KEY, characteristics: ["ip.src"], // track requests by IP address rules: [ slidingWindow({ mode: "LIVE", // will block requests. Use "DRY_RUN" to log only match: "/api/hello", // match all requests to /api/hello interval: 60, // 60 second sliding window max: 100, // allow a maximum of 100 requests }), ],});
Token bucket rate limit options
Based on a bucket filled with a specific number of tokens. Each request withdraws a token from the bucket and the bucket is refilled at a fixed rate. Once the bucket is empty, the client is blocked until the bucket refills. Options are explained in the Configuration documentation. See the token bucket algorithm description for more details about how the algorithm works.
// Options for token bucket rate limit// See https://docs.arcjet.com/rate-limiting/configurationtype TokenBucketRateLimitOptions = { mode?: "LIVE" | "DRY_RUN"; // "LIVE" will block requests. "DRY_RUN" will log only match?: string; // request path the rate limit applies to characteristics?: string[]; // how the client is identified. Defaults to the global characteristics if unset refillRate: number; // number of tokens to add to the bucket at each interval interval: number; // the interval in seconds to add tokens to the bucket capacity: number; // the maximum number of tokens the bucket can hold};
Token bucket example
See the token bucket example for how to specify the number of tokens to request.
import arcjet, { tokenBucket } from "@arcjet/node";
const aj = arcjet({ key: process.env.ARCJET_KEY, characteristics: ["ip.src"], // track requests by IP address rules: [ tokenBucket({ mode: "LIVE", // will block requests. Use "DRY_RUN" to log only match: "/api/hello", // match all requests to /api/hello refillRate: 10, // refill 10 tokens per interval interval: 60, // 60 second interval capacity: 100, // bucket maximum capacity of 100 tokens }), ],});
Identifying users
Rate limit rules use characteristics
to identify the client and apply the
limit across requests. The default is to use the client’s IP address. However,
you can specify other
characteristics such as a user
ID or other metadata from your application.
In this example we define a rate limit rule that applies to a specific user ID.
The custom characteristic is userId
with the value passed as a prop on the
protect
function. You can use any string for the characteristic name and any
string
, number
or boolean
for the value.
import arcjet, { fixedWindow } from "@arcjet/node";import http from "node:http";
const aj = arcjet({ key: process.env.ARCJET_KEY!, // Get your site key from https://app.arcjet.com // Define a custom userId characteristic. // See https://docs.arcjet.com/rate-limiting/configuration#characteristics characteristics: ["userId"], rules: [ fixedWindow({ mode: "LIVE", window: "1h", max: 60, }), ],});
const server = http.createServer(async function ( req: http.IncomingMessage, res: http.ServerResponse,) { // Pass userId as a string to identify the user. This could also be a number // or boolean value const decision = await aj.protect(req, { userId: "user123" }); console.log("Arcjet decision", decision);
if (decision.isDenied()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end( JSON.stringify({ error: "Too Many Requests", reason: decision.reason }), ); } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello world" })); }});
server.listen(8000);
import arcjet, { fixedWindow } from "@arcjet/node";import http from "node:http";
const aj = arcjet({ key: process.env.ARCJET_KEY, // Get your site key from https://app.arcjet.com // Define a custom userId characteristic. // See https://docs.arcjet.com/rate-limiting/configuration#characteristics characteristics: ["userId"], rules: [ fixedWindow({ mode: "LIVE", window: "1h", max: 60, }), ],});
const server = http.createServer(async function (req, res) { // Pass userId as a string to identify the user. This could also be a number // or boolean value const decision = await aj.protect(req, { userId: "user123" }); console.log("Arcjet decision", decision);
if (decision.isDenied()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end( JSON.stringify({ error: "Too Many Requests", reason: decision.reason }), ); } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello world" })); }});
server.listen(8000);
Rules
The arcjet
client is configured with one or more rules which take one or many
of the above options.
Example - single rate limit
Set a single rate limit rule on the /api/hello
API route that applies a 60
request limit per hour per IP address (the default if no characteristics
are
specified).
import arcjet, { fixedWindow } from "@arcjet/node";
const aj = arcjet({ key: process.env.ARCJET_KEY, rules: [ fixedWindow({ mode: "LIVE", match: "/api/hello", window: "1h", max: 60, }), ],});
Example - dry run mode for new rules
Rate limits can be combined in the arcjet
client which allows you to test new
configurations in dry run mode first before enabling them in live mode. You can
inspect the results of each rule by logging them or using the Arcjet
Dashboard.
import arcjet, { fixedWindow } from "@arcjet/node";
const aj = arcjet({ key: process.env.ARCJET_KEY, characteristics: ["ip.src"], rules: [ fixedWindow( // This rule is live { mode: "LIVE", match: "/api/hello", window: "1h", max: 60, }, // This rule is in dry run mode, so will log but not block { mode: "DRY_RUN", match: "/api/hello", characteristics: ['http.request.headers["x-api-key"]'], window: "1h", // max could also be a dynamic value applied after looking up a limit // elsewhere e.g. in a database for the authenticated user max: 600, }, ), ],});
Decision
Arcjet provides a single protect
function that is used to execute your
protection rules. This requires a request
argument which is the request
context as passed to the request handler.
This function returns a Promise
that resolves to an
ArcjetDecision
object. This contains the following properties:
id
(string
) - The unique ID for the request. This can be used to look up the request in the Arcjet dashboard. It is prefixed withreq_
for decisions involving the Arcjet cloud API. For decisions taken locally, the prefix islreq_
.conclusion
(ArcjetConclusion
) - The final conclusion based on evaluating each of the configured rules. If you wish to accept Arcjet’s recommended action based on the configured rules then you can use this property.reason
(ArcjetReason
) - An object containing more detailed information about the conclusion.results
(ArcjetRuleResult[]
) - An array ofArcjetRuleResult
objects containing the results of each rule that was executed.ip
(ArcjetIpDetails
) - An object containing Arcjet’s analysis of the client IP address. See IP analysis in the SDK reference for more information.
See the SDK reference for more details about the rule results.
You check if a deny conclusion has been returned by a rate limit rule by using
decision.isDenied()
and decision.reason.isRateLimit()
.
You can iterate through the results and check whether a rate limit was applied:
for (const result of decision.results) { console.log("Rule Result", result);}
This example will log the full result as well as each rate limit rule:
import arcjet, { fixedWindow, detectBot } from "@arcjet/node";import http from "node:http";
const aj = arcjet({ key: process.env.ARCJET_KEY!, // Get your site key from https://app.arcjet.com characteristics: ["ip.src"], rules: [ fixedWindow({ mode: "LIVE", window: "1h", max: 60, }), detectBot({ mode: "LIVE", block: ["AUTOMATED", "LIKELY_AUTOMATED"], }), ],});
const server = http.createServer(async function ( req: http.IncomingMessage, res: http.ServerResponse,) { const decision = await aj.protect(req);
for (const result of decision.results) { console.log("Rule Result", result);
if (result.reason.isRateLimit()) { console.log("Rate limit rule", result); }
if (result.reason.isBot()) { console.log("Bot protection rule", result); } }
if (decision.isDenied()) { if (decision.reason.isRateLimit()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end( JSON.stringify({ error: "Too Many Requests", reason: decision.reason }), ); res.end(JSON.stringify({ error: "Forbidden" })); } else { res.writeHead(403, { "Content-Type": "application/json" }); res.end(JSON.stringify({ error: "Forbidden" })); } } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello world" })); }});
server.listen(8000);
import arcjet, { fixedWindow, detectBot } from "@arcjet/node";import http from "node:http";
const aj = arcjet({ key: process.env.ARCJET_KEY, // Get your site key from https://app.arcjet.com characteristics: ["ip.src"], rules: [ fixedWindow({ mode: "LIVE", window: "1h", max: 60, }), detectBot({ mode: "LIVE", block: ["AUTOMATED", "LIKELY_AUTOMATED"], }), ],});
const server = http.createServer(async function (req, res) { const decision = await aj.protect(req);
for (const result of decision.results) { console.log("Rule Result", result);
if (result.reason.isRateLimit()) { console.log("Rate limit rule", result); }
if (result.reason.isBot()) { console.log("Bot protection rule", result); } }
if (decision.isDenied()) { if (decision.reason.isRateLimit()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end( JSON.stringify({ error: "Too Many Requests", reason: decision.reason }), ); res.end(JSON.stringify({ error: "Forbidden" })); } else { res.writeHead(403, { "Content-Type": "application/json" }); res.end(JSON.stringify({ error: "Forbidden" })); } } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello world" })); }});
server.listen(8000);
Token bucket request
When using a token bucket rule, an additional requested
prop should be passed
to the protect
function. This is the number of tokens the client is requesting
to withdraw from the bucket.
import arcjet, { tokenBucket } from "@arcjet/node";import http from "node:http";
const aj = arcjet({ key: process.env.ARCJET_KEY!, // Get your site key from https://app.arcjet.com characteristics: ["ip.src"], rules: [ tokenBucket({ mode: "LIVE", refillRate: 40_000, interval: "1d", capacity: 40_000, }), ],});
const server = http.createServer(async function ( req: http.IncomingMessage, res: http.ServerResponse,) { const decision = await aj.protect(req, { requested: 50 }); console.log("Arcjet decision", decision);
if (decision.isDenied()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end( JSON.stringify({ error: "Too Many Requests", reason: decision.reason }), ); } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello world" })); }});
server.listen(8000);
import arcjet, { tokenBucket } from "@arcjet/node";import http from "node:http";
const aj = arcjet({ key: process.env.ARCJET_KEY, // Get your site key from https://app.arcjet.com characteristics: ["ip.src"], rules: [ tokenBucket({ mode: "LIVE", refillRate: 40_000, interval: "1d", capacity: 40_000, }), ],});
const server = http.createServer(async function (req, res) { const decision = await aj.protect(req, { requested: 50 }); console.log("Arcjet decision", decision);
if (decision.isDenied()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end( JSON.stringify({ error: "Too Many Requests", reason: decision.reason }), ); } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello world" })); }});
server.listen(8000);
Rate limit headers
With a rate limit rule enabled, you can access additional metadata in every Arcjet decision result:
max
(number
): The configured maximum number of requests applied to this request.remaining
(number
): The number of requests remaining beforemax
is reached within the window.window
(number
): The total amount of seconds in which requests are counted.reset
(number
): The remaining amount of seconds in the window.
These can be used to return RateLimit
HTTP headers (draft
RFC) to
offer the client more detail.
We provide the @arcjet/decorate
package for decorating
your responses with appropriate RateLimit
headers based on a decision.
import arcjet, { fixedWindow } from "@arcjet/node";import { setRateLimitHeaders } from "@arcjet/decorate";import http from "node:http";
const aj = arcjet({ key: process.env.ARCJET_KEY!, // Get your site key from https://app.arcjet.com // Tracking by ip.src is the default if not specified //characteristics: ["ip.src"], rules: [ fixedWindow({ mode: "LIVE", window: "1h", max: 60, }), ],});
const server = http.createServer(async function ( req: http.IncomingMessage, res: http.ServerResponse,) { const decision = await aj.protect(req); console.log("Arcjet decision", decision);
setRateLimitHeaders(res, decision);
if (decision.isDenied()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end( JSON.stringify({ error: "Too Many Requests", reason: decision.reason }), ); } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello world" })); }});
server.listen(8000);
import arcjet, { fixedWindow } from "@arcjet/node";import { setRateLimitHeaders } from "@arcjet/decorate";import http from "node:http";
const aj = arcjet({ key: process.env.ARCJET_KEY, // Get your site key from https://app.arcjet.com // Tracking by ip.src is the default if not specified //characteristics: ["ip.src"], rules: [ fixedWindow({ mode: "LIVE", window: "1h", max: 60, }), ],});
const server = http.createServer(async function (req, res) { const decision = await aj.protect(req); console.log("Arcjet decision", decision);
setRateLimitHeaders(res, decision);
if (decision.isDenied()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end( JSON.stringify({ error: "Too Many Requests", reason: decision.reason }), ); } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello world" })); }});
server.listen(8000);
Error handling
Arcjet is designed to fail open so that a service issue or misconfiguration does
not block all requests. The SDK will also time out and fail open after 500ms
when NODE_ENV
is production
and 1000ms otherwise. However, in most cases,
the response time will be less than 20-30ms.
If there is an error condition, Arcjet will return an ERROR
conclusion
.
import arcjet, { tokenBucket } from "@arcjet/node";import http from "node:http";
const aj = arcjet({ key: process.env.ARCJET_KEY!, // Get your site key from https://app.arcjet.com characteristics: ["userId"], // track requests by a custom user ID rules: [ // Create a token bucket rate limit. Other algorithms are supported. tokenBucket({ mode: "LIVE", // will block requests. Use "DRY_RUN" to log only refillRate: 5, // refill 5 tokens per interval interval: 10, // refill every 10 seconds capacity: 10, // bucket maximum capacity of 10 tokens }), ],});
const server = http.createServer(async function ( req: http.IncomingMessage, res: http.ServerResponse,) { const userId = "user123"; // Replace with your authenticated user ID const decision = await aj.protect(req, { userId, requested: 5 }); // Deduct 5 tokens from the bucket console.log("Arcjet decision", decision);
if (decision.isErrored()) { // Fail open by logging the error and continuing console.warn("Arcjet error", decision.reason.message); // You could also fail closed here for very sensitive routes //res.writeHead(503, { "Content-Type": "application/json" }); //res.end(JSON.stringify({ error: "Service unavailable" })); }
if (decision.isDenied()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end( JSON.stringify({ error: "Too Many Requests", reason: decision.reason }), ); } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello world" })); }});
server.listen(8000);
import arcjet, { tokenBucket } from "@arcjet/node";import http from "node:http";
const aj = arcjet({ key: process.env.ARCJET_KEY, // Get your site key from https://app.arcjet.com characteristics: ["userId"], // track requests by a custom user ID rules: [ // Create a token bucket rate limit. Other algorithms are supported. tokenBucket({ mode: "LIVE", // will block requests. Use "DRY_RUN" to log only refillRate: 5, // refill 5 tokens per interval interval: 10, // refill every 10 seconds capacity: 10, // bucket maximum capacity of 10 tokens }), ],});
const server = http.createServer(async function (req, res) { const userId = "user123"; // Replace with your authenticated user ID const decision = await aj.protect(req, { userId, requested: 5 }); // Deduct 5 tokens from the bucket console.log("Arcjet decision", decision);
if (decision.isErrored()) { // Fail open by logging the error and continuing console.warn("Arcjet error", decision.reason.message); // You could also fail closed here for very sensitive routes //res.writeHead(503, { "Content-Type": "application/json" }); //res.end(JSON.stringify({ error: "Service unavailable" })); }
if (decision.isDenied()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end( JSON.stringify({ error: "Too Many Requests", reason: decision.reason }), ); } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello world" })); }});
server.listen(8000);
Examples
Rate limit by IP address
The example below shows how to configure a rate limit on a single API route. It applies a limit of 60 requests per hour per IP address. If the limit is exceeded, the client is blocked for 10 minutes before being able to make any further requests.
Applying a rate limit by IP address is the default if no
characteristics
are specified.
import arcjet, { fixedWindow } from "@arcjet/node";import http from "node:http";
const aj = arcjet({ key: process.env.ARCJET_KEY!, // Get your site key from https://app.arcjet.com // Tracking by ip.src is the default if not specified //characteristics: ["ip.src"], rules: [ fixedWindow({ mode: "LIVE", window: "1h", max: 60, }), ],});
const server = http.createServer(async function ( req: http.IncomingMessage, res: http.ServerResponse,) { const decision = await aj.protect(req); console.log("Arcjet decision", decision);
if (decision.isDenied()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end( JSON.stringify({ error: "Too Many Requests", reason: decision.reason }), ); } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello world" })); }});
server.listen(8000);
import arcjet, { fixedWindow } from "@arcjet/node";import http from "node:http";
const aj = arcjet({ key: process.env.ARCJET_KEY, // Get your site key from https://app.arcjet.com // Tracking by ip.src is the default if not specified //characteristics: ["ip.src"], rules: [ fixedWindow({ mode: "LIVE", window: "1h", max: 60, }), ],});
const server = http.createServer(async function (req, res) { const decision = await aj.protect(req); console.log("Arcjet decision", decision);
if (decision.isDenied()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end( JSON.stringify({ error: "Too Many Requests", reason: decision.reason }), ); } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello world" })); }});
server.listen(8000);
Rate limit by IP address with custom response
The example below is the same as the one above. However this example also shows a customized response rather than the default
import arcjet, { fixedWindow } from "@arcjet/node";import http from "node:http";
const aj = arcjet({ key: process.env.ARCJET_KEY!, // Get your site key from https://app.arcjet.com // Tracking by ip.src is the default if not specified //characteristics: ["ip.src"], rules: [ fixedWindow({ mode: "LIVE", window: "1h", max: 60, }), ],});
const server = http.createServer(async function ( req: http.IncomingMessage, res: http.ServerResponse,) { const decision = await aj.protect(req); console.log("Arcjet decision", decision);
if (decision.isDenied()) { if (decision.reason.isRateLimit()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end( JSON.stringify({ error: "Too Many Requests", reason: decision.reason }), ); } else { res.writeHead(403, { "Content-Type": "application/json" }); res.end(JSON.stringify({ error: "Forbidden", reason: decision.reason })); } } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello world" })); }});
server.listen(8000);
import arcjet, { fixedWindow } from "@arcjet/node";import http from "node:http";
const aj = arcjet({ key: process.env.ARCJET_KEY, // Get your site key from https://app.arcjet.com // Tracking by ip.src is the default if not specified //characteristics: ["ip.src"], rules: [ fixedWindow({ mode: "LIVE", window: "1h", max: 60, }), ],});
const server = http.createServer(async function (req, res) { const decision = await aj.protect(req); console.log("Arcjet decision", decision);
if (decision.isDenied()) { if (decision.reason.isRateLimit()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end( JSON.stringify({ error: "Too Many Requests", reason: decision.reason }), ); } else { res.writeHead(403, { "Content-Type": "application/json" }); res.end(JSON.stringify({ error: "Forbidden", reason: decision.reason })); } } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello world" })); }});
server.listen(8000);
Rate limit by API key header
APIs are commonly protected by keys. You may wish to apply a rate limit based on the key, regardless of which IPs the requests come from. To achieve this, you can specify the characteristics Arcjet will use to track the limit.
The example below shows how to configure a rate limit on a single API route. It
applies a limit of 60 requests per hour per API key, where the key is provided
in a custom header called x-api-key
. If the limit is exceeded, the client is
blocked for 10 minutes before being able to make any further requests.
import arcjet, { fixedWindow } from "@arcjet/node";
const aj = arcjet({ key: process.env.ARCJET_KEY, characteristics: ['http.request.headers["x-api-key"]'], rules: [ fixedWindow({ mode: "LIVE", window: "1h", max: 60, }), ],});
Express server route protection
If you’re using Express, you can use Arcjet in the same way as the examples above:
import arcjet, { fixedWindow } from "@arcjet/node";import express from "express";
const app = express();const port = 3000;
const aj = arcjet({ // Get your site key from https://app.arcjet.com and set it as an environment // variable rather than hard coding. key: process.env.ARCJET_KEY, // Tracking by ip.src is the default if not specified //characteristics: ["ip.src"], rules: [ // Fixed window rate limit. Arcjet also supports sliding window and token // bucket. fixedWindow({ mode: "LIVE", // will block requests. Use "DRY_RUN" to log only window: "1m", // 1 min fixed window max: 1, // allow a single request (for demo purposes) }), ],});
app.get("/", async (req, res) => { const decision = await aj.protect(req);
if (decision.isDenied()) { res.writeHead(429, { "Content-Type": "application/json" }); res.end(JSON.stringify({ error: "Too Many Requests" })); } else { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ message: "Hello World" })); }});
app.listen(port, () => { console.log(`Example app listening on port ${port}`);});