ASP.NET Core guide · .NET SDK

ASP.NET Core rate limiting,per API key and per plan.

AddReqKey and UseReqKey. Every request is checked against the caller’s key, charged against their credits, and held to their plan’s limit — across every instance.

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

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The usual ASP.NET Core rate limiter counts requests. It doesn’t know your customers.

Since .NET 7, AddRateLimiter registers fixed-window, sliding-window, token-bucket, and concurrency limiters, applied per endpoint with RequireRateLimiting.

With Microsoft.AspNetCore.RateLimitingtoday
// Program.cs — built-in rate limitingbuilder.Services.AddRateLimiter(options =>
{
    options.RejectionStatusCode = StatusCodes.Status429TooManyRequests;
    options.AddFixedWindowLimiter("fixed", limiter =>
    {
        limiter.PermitLimit = 100;
        limiter.Window = TimeSpan.FromMinutes(1);
    });
});

app.UseRateLimiter();
app.MapGet("/search", Search).RequireRateLimiting("fixed");
  • Limiter state is in memory — each instance behind the load balancer counts alone
  • Per-customer limits need a partitioned limiter keyed on something you trust
  • 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 ASP.NET Coreone 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
Endpoints read the verdict with HttpContext.GetReqKeyDecision(). See the code

ASP.NET Core 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

    dotnet add package ReqKey.AspNetCore

  2. 2

    Set your project key

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

  3. 3

    Add the ASP.NET Core middleware

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

Program.csdotnet add package ReqKey.AspNetCore
using ReqKey.AspNetCore;
 
var builder = WebApplication.CreateBuilder(args);
 
builder.Services.AddReqKey(options =>
{
    options.ProjectKey = builder.Configuration["REQKEY_PROJECT_KEY"];
    options.ApiId = "api_payments";
    options.KeyName = "X-Startup-Key";
    options.ExcludePaths = ["/health"];
});
 
var app = builder.Build();
app.UseRouting();
app.UseReqKey();
 
app.MapPost("/payments", (HttpContext context) => Results.Ok(new
{
    creditsRemaining = context.GetReqKeyDecision()?.CreditsRemaining,
}))
    .RequireReqKey(credits: 5, apiId: "api_images", resource: "/v1/images");
 
app.MapGet("/health", () => Results.Ok(new { ok = true })).SkipReqKey();
 
app.Run();
Also in .NET: ASP.NET Core Web APIFull .NET 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 .NET:

Per-route credits · .NET
// Exact paths or trailing-* prefixes: never validated, charged, or recorded
options.ExcludePaths = ["/health", "/docs/*"];
 
// Or decide per request with a predicate
options.ShouldProtect = (context, _) =>
    ValueTask.FromResult(context.Request.Path.StartsWithSegments("/api"));
 
// Charge different endpoints differently
options.CreditCostResolver = (context, _) =>
    ValueTask.FromResult(context.Request.Method == HttpMethods.Post ? 5 : 1);
 
// Minimal APIs and MVC actions override cost per endpoint
app.MapPost("/images", HandleImage).RequireReqKey(credits: 5, apiId: "api_images");
// [ReqKey(Credits = 2, Resource = "/v1/orders")] on a controller action

Rate limits

Set limits on plans, not in code.

Your ASP.NET Core 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 ASP.NET Core teams hit in production.

Per-endpoint cost

.RequireReqKey(credits: 5) on a Minimal API endpoint charges more for expensive routes.

Options or appsettings.json

Configure in code with an options lambda, or bind from configuration — resolvers stay in code.

Health checks

Add "/health" to ExcludePaths so probes are never validated or counted.

ASP.NET Core rate limiting: the questions teams ask.

Something else? Ask the team or read the docs.

  • Keep it for concurrency limits or anonymous endpoints if you use them. Customer plan limits and credits come from ReqKey.

  • The packages target .NET 8.

  • 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 ASP.NET Core 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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