TL;DR: I bundled 16 tools every online seller needs into one API — marketplace fee calculators (Amazon, eBay, Etsy), profit/pricing math, barcode product lookup, and listing helpers (SEO titles, descriptions, SKUs). It's live on RapidAPI with a free tier. Here's how it works.
The problem
If you sell online — dropshipping, Amazon FBA, Etsy, your own store — you constantly ask the same questions:
- After fees, what's my actual profit on this item?
- What price do I need to hit a 40% margin?
- How many units until I break even?
- What's this product, given its barcode?
Each is a small calculation, but wiring them up (correctly, and per marketplace) is tedious. So I built eCommerce Seller Toolkit — one API that answers all of them.
What's inside (16 endpoints)
| Group | Endpoints |
|---|---|
| Marketplace fees |
/fees/amazon, /fees/ebay, /fees/etsy
|
| Pricing & profit |
/pricing/margin, /discount, /dropshipping, /order, /breakeven, /suggest
|
| Products |
/barcode/lookup, /barcode/validate, /barcode/generate
|
| Listings |
/product/title, /product/description, /sku/generate
|
Everything returns clean JSON and is 100% legal — product data comes from the open ODbL database, not scraping.
Example: true profit after Amazon fees
GET /fees/amazon?price=25&category=standard&weight=1&cost=8
{
"price": 25,
"fees": { "referral_fee": 3.75, "fba_fee": 4.13, "total_fees": 7.88 },
"cost": 8,
"net_profit": 9.12,
"margin_percent": 36.48
}
One request and you know exactly what you keep.
Example: what price hits my target margin?
GET /pricing/suggest?cost=20&target_margin=40
{ "cost": 20, "suggested_price": 33.33, "profit": 13.33, "markup_percent": 66.67 }
The math is simple but easy to get wrong (margin vs markup trips people up constantly):
// margin is a % of the selling price, not of cost
const price = cost / (1 - targetMargin / 100);
Example: real product data from a barcode
GET /barcode/lookup?barcode=737628064502
{
"found": true,
"product": {
"name": "Thai peanut noodle kit",
"brand": "Simply Asia, Thai Kitchen",
"category": "Noodles, Rice Noodles",
"image": "https://images.openfoodfacts.org/.../front_en.400.jpg"
},
"source": "Open Food Facts (open data, ODbL)"
}
The stack
- Node.js + Express — simple and fast to ship.
- Vercel (serverless) — free, public HTTPS, zero config.
- RapidAPI — billing, keys, rate limiting and the marketplace.
No database needed — every endpoint is either a pure calculation or a call to an open-data source.
Try it
Free tier (500 requests/month), no credit card:
👉 eCommerce Seller Toolkit on RapidAPI
What seller tool should I add next? Let me know in the comments 👇
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