Fastify guide · Node.js SDK

Fastify rate limiting,one plugin, every customer.

Register the ReqKey plugin and every route is checked against the caller’s key, charged against their credits, and held to their plan’s rate limit.

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  • Keys issued per customer
  • Credits that refill
  • Limits per plan, not per process

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API requests validated
100M+
Average key validation
<5ms
Average analytics ingest
<5ms
Check and log, end to end
<10ms

The usual Fastify rate limiter counts requests. It doesn’t know your customers.

The official plugin sets a max per time window, keyed by IP unless you pass a keyGenerator, with a Redis option for multi-instance deployments.

With @fastify/rate-limittoday
// server.ts — with @fastify/rate-limitimport rateLimit from "@fastify/rate-limit";

await app.register(rateLimit, {
  max: 100,
  timeWindow: "1 minute",
  keyGenerator: (request) =>
    (request.headers["x-api-key"] as string) ?? request.ip,
});
  • Counters live in process memory — every worker and every instance keeps its own count
  • Needs Redis (or another shared store) before the limit is correct on more than one server
  • Any header value gets a bucket — the key itself is never checked
  • No API keys: issuing, hashing, scoping, and revoking them is still yours to build
  • No credit balance: a request can’t cost 5 on one route and 1 on another, or refill each month
  • One limit for everyone — no per-plan limits for Free, Pro, and Enterprise customers
With ReqKey in Fastifyone middleware
  • API keys issued per customer, prefixed, hashed, and revocable from the dashboard
  • A credit balance per customer — price each route, refill every hour, day, week, or month
  • Rate limits set per plan, shared by all of a customer’s keys, from 1 second to 24 hours
  • The same count on every worker, instance, and region — no Redis to run
  • Over the limit? A 429 with Retry-After, and no credits charged
  • Every request logged per customer — status, latency, endpoint — in under 5ms
Your handler reads the verdict from request.reqkey. See the code

Fastify in three steps, one of them code.

ReqKey runs inside your API, not in front of it. Your server asks one question per request and gets an answer in under 5ms.

  1. 1

    Install the SDK

    npm install reqkey fastify

  2. 2

    Set your project key

    Copy it from the dashboard into REQKEY_PROJECT_KEY. It stays on your server.

  3. 3

    Add the Fastify middleware

    Every request is checked, charged, and logged before your handler runs.

server.tsnpm install reqkey fastify
import Fastify, { type FastifyRequest } from "fastify";
import type { VerificationResult } from "reqkey";
import reqkey from "reqkey/fastify";
 
const app = Fastify();
 
await app.register(reqkey, {
  projectKey: process.env.REQKEY_PROJECT_KEY,
  apiId: "api_payments",
  mode: "both",
  keyName: "x-startup-key",
  excludePaths: ["/health"],
});
 
app.post("/payments", async (request) => {
  const decision = (request as FastifyRequest & { reqkey?: VerificationResult }).reqkey;
  return { created: true, creditsRemaining: decision?.creditsRemaining };
});
 
await app.listen({ port: 3000 });
Also in Node.js: Express, Next.js, NestJS, Hono, KoaFull Node.js reference

Every request gets one of these answers

  • 200Valid key, credits charged — your handler runs
  • 402Out of credits
  • 403Key disabled, or not allowed on this API
  • 429Over the rate limit — no credits charged

Where ReqKey sits

Your customer
Your APIReqKey, under 5ms
Your handler

Responses go straight back to your customer. ReqKey sees the key check and the log line, nothing else.

Credits

Charge each route what it costs you.

A lookup can cost 1 credit and a render 5, from the same balance. Excluded paths are never validated, charged, or recorded. In Node.js:

Per-route credits · Node.js
// Exact paths or trailing-* prefixes: never validated, charged, or recorded
excludePaths: ["/health", "/openapi.json", "/docs/*", "/cron/*"]
 
// Or decide per request with a sync or async resolver
shouldProtect: ({ path }) => path.startsWith("/api/")
 
// Charge different endpoints differently (non-negative integers)
credits: ({ method, path }) => {
  if (method === "POST" && path === "/images") return 5;
  if (path.startsWith("/reports/")) return 2;
  return 1;
}

Rate limits

Set limits on plans, not in code.

Your Fastify code never hard-codes a number. Each plan carries its credits, refill, and rate limit; moving a customer to Pro changes all three with no deploy.

PlanCreditsRate limit
Free1,000 / month5 req / s
Pro50,000 / month50 req / s
Scale1,000,000 / month500 req / s
429Over the limit, a call is answered with Retry-After and costs nothing — no credits and no quota.

Example plans. You name them and pick the numbers.

Notes for Fastify teams hit in production.

Registered once, applied everywhere

await app.register(reqkey, options) applies to the whole instance — the plugin skips Fastify’s encapsulation on purpose, so routes in child plugins are covered too.

Built for Fastify’s speed

A check averages under 5ms, so the plugin fits Fastify’s budget without an extra hop through a gateway.

Exclude what’s public

excludePaths keeps /health, /docs, and webhooks open — they are never validated, charged, or recorded.

Fastify rate limiting: the questions teams ask.

Something else? Ask the team or read the docs.

  • No. ReqKey keeps the counts, so every Fastify instance sees the same balance and limit for a customer.

  • Yes — pass a credits function that returns a cost per method and path.

  • On their plan or on the customer (consumer) in ReqKey — a number of requests per window from 1 second to 24 hours, shared by all of that customer’s keys. Your Fastify code never hard-codes a limit, so upgrading a customer is a dashboard change, not a deploy.

  • A check averages under 5ms. ReqKey runs inside your app as middleware, not as a gateway in front of it, so responses go straight back to your customer.

  • You choose: fail closed and answer 503, or fail open and let requests through. Invalid keys are denied either way, and a validation is never retried, so no one is charged twice.

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