Slim guide · PHP SDK

Slim rate limiting,as one PSR-15 middleware.

Add the ReqKey middleware to your Slim app. Every request is checked against the caller’s key, charged against their credits, and held to their plan’s limit.

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

Official SDKs with drop-in middleware for the stack you already run

  • Python
  • Node.js
  • Go
  • Rust
  • PHP
  • .NET
  • Java
API requests validated
100M+
Average key validation
<5ms
Average analytics ingest
<5ms
Check and log, end to end
<10ms

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

Slim ships no limiter. Teams add a community PSR-15 middleware or wire Symfony’s RateLimiter component in by hand, backed by APCu or Redis.

With a PSR-15 limitertoday
  • APCu is per server; Redis is one more thing to run
  • Keyed by IP address by default, not by the customer who is paying
  • 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
  • No per-customer usage log to answer “why was I blocked?” or bill against
With ReqKey in Slimone 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
Route callbacks read the verdict with $request->getAttribute('reqkey'). See the code

Slim 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

    composer require reqkey/reqkey slim/slim slim/psr7

  2. 2

    Set your project key

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

  3. 3

    Add the Slim middleware

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

index.phpcomposer require reqkey/reqkey slim/slim slim/psr7
use ReqKey\Client;
use ReqKey\Config\ClientConfig;
use ReqKey\Config\MiddlewareConfig;
use ReqKey\Integration\Psr15\ReqKeyMiddleware;
use ReqKey\MiddlewareProcessor;
use Slim\Factory\AppFactory;
 
$app = AppFactory::create();
 
$app->get('/payments', function ($request, $response) {
    $decision = $request->getAttribute('reqkey');
    $response->getBody()->write(json_encode([
        'credits_remaining' => $decision->creditsRemaining,
    ], JSON_THROW_ON_ERROR));
 
    return $response->withHeader('Content-Type', 'application/json');
});
 
$app->addRoutingMiddleware();
$app->add(new ReqKeyMiddleware(new MiddlewareProcessor(
    new Client(ClientConfig::fromEnvironment()),
    new MiddlewareConfig(apiId: 'api_payments', keyName: 'X-Startup-Key'),
)));
$app->run();
Also in PHP: Laravel, SymfonyFull PHP 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 PHP:

Per-route credits · PHP
new MiddlewareConfig(
    apiId: 'api_payments',
    // Exact paths or trailing-* prefixes: never validated, charged, or recorded
    excludePaths: ['/health', '/docs/*'],
    // Or decide per request with a predicate
    shouldProtect: static fn (RequestData $request): bool => str_starts_with($request->path, '/api/'),
    // Charge endpoints differently — a closure instead of an int
    credits: static fn (RequestData $request): int => $request->path === '/images' ? 5 : 1,
);

Rate limits

Set limits on plans, not in code.

Your Slim 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 Slim teams hit in production.

Standard PSR-15

The same middleware works in Mezzio or any PSR-15 pipeline — nothing Slim-specific.

Runs before your routes

Slim runs middleware last-in, first-out, so adding it after addRoutingMiddleware() puts the key check ahead of routing.

Custom messages

errorMessages rewrites the customer-facing text per denial code while keeping the stable code.

Slim rate limiting: the questions teams ask.

Something else? Ask the team or read the docs.

  • Slim 4 needs one anyway — slim/psr7 in the install command covers it.

  • Yes. Nothing is kept between requests in PHP, so FPM, RoadRunner, and FrankenPHP all enforce the same limit.

  • 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 Slim 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.

More PHP guides.

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