How to use the Seller Fee API in C#

Marketplace and payment fees for Gumroad, Etsy, Stripe and PayPal with net payout breakdowns. This guide calls it from C# with code we've run against the live endpoint.

Online · 1566 msEndpoint tested Nov 15, 2026

1. What you need

.NET 6 or newer. Paste into a top-level `Program.cs` and run `dotnet run`.

No API key or sign-up. Endpoint: https://seller-fee-api.narwhalapis.workers.dev

2. Make the request

using System.Net.Http;

using var http = new HttpClient { Timeout = TimeSpan.FromSeconds(10) };
var json = await http.GetStringAsync("https://seller-fee-api.narwhalapis.workers.dev");
Console.WriteLine(json);

3. The response

Trimmed from the live response on Nov 15, 2026.

JSON

{
  "name": "Seller Fee API",
  "description": "Fees, net payout and effective rate for Gumroad, Etsy, Stripe and PayPal, plu...",
  "endpoints": [
    "/v1/platforms",
    "/v1/fee",
    "/v1/price"
  ],
  "example": "/v1/compare?amount=20",
  "links": {
    "docs": "https://narwhalthepong.github.io/gumroad-license-check/free-tax-finance-api",
    "rapidapi": "https://rapidapi.com/narwhalapis/api/seller-fee-api-gumroad-etsy-stripe-paypa...",
    "openapi": "/openapi.json",
    "spreadsheet": "https://payhip.com/b/6tHXR"
  },
  "free": "Free to use; please keep request rates reasonable.",
  "version": "1.1.0"
}

4. Before you ship

Set a timeout and handle non-200 responses: free APIs can rate-limit or go down.
Cache responses where you can, instead of calling the API on every page view.
Read the official documentation ↗ for rate limits and terms of use.

FAQ

Does the Seller Fee API need an API key in C#?

No. The Seller Fee API works without an API key, so the C# example runs as-is.

Can I call the Seller Fee API from the browser?

Yes. It sends CORS headers, so front-end JavaScript can call it directly.

What does the Seller Fee API return?

JSON. The example response on this page is trimmed from a real response our health check received on Nov 15, 2026.

Same API in: Python · JavaScript · Node.js · PHP · Java · Go · Ruby
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