
Seller fee schedules for 21 e-commerce marketplaces and payment processors as JSON.
Marketplace Fee Data API is a free Shopping API that requires no API key, is served over HTTPS and supports CORS, so it can be called from the browser.
Free JSON API of marketplace and payment fee schedules — Amazon, eBay, Etsy, PayPal, Stripe and 16 more platforms. CC BY 4.0, no key, CORS enabled.
Details from sellerscalc.com.

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The Marketplace Fee Data API is provided by SellersCalc — E-commerce Calculators (sellerscalc.com). Free JSON API of marketplace and payment fee schedules — Amazon, eBay, Etsy, PayPal, Stripe and 16 more platforms. CC BY 4.0, no key, CORS enabled.
Yes. The Marketplace Fee Data API is listed in the Shopping category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
No. The Marketplace Fee Data API requires no authentication, so you can start making requests without signing up.
Yes. The Marketplace Fee Data API supports CORS, so front-end JavaScript can call it directly.
Yes. The Marketplace Fee Data API is served over HTTPS, so it's safe to use in production.