DEV Community: Manal166

I built an eCommerce Seller Toolkit API: Amazon/eBay/Etsy fees, pricing & product data in one place

Manal166 — Sun, 14 Jun 2026 23:35:29 +0000

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 👇

I added 3 new tools to my Social Media API: caption generator, post optimizer & username generator

Manal166 — Sun, 07 Jun 2026 20:15:39 +0000

A few weeks ago I launched Social Media Toolkit — one API bundling 8 social media utilities. Based on feedback, I just shipped 3 new tools. Here's what they do and how they work.

If you missed the first post, the API does things like username availability, hashtag generation, engagement rate and best-time-to-post — all in one place, no scraping. Today I'm adding three tools that round out the content workflow: write it, score it, brand it.

1. Caption Generator — write the post

Give it a topic and a tone, get ready-to-post captions back — each with a hook, emojis, a call-to-action and matching hashtags.

GET /caption/generate?topic=fitness&tone=inspirational&count=2

{
  "topic": "fitness",
  "tone": "inspirational",
  "captions": [
    {
      "text": "Every expert in Fitness was once a beginner. 🚀\n\nShow up for your fitness dreams, one step at a time. ❤️\n\nTag someone who needs this.",
      "hashtags": ["#fitness", "#workout", "#gym", "#fitnessmotivation"]
    }
  ]
}

Five tones are supported: casual, professional, funny, inspirational, promotional. The whole thing is template-based and deterministic — no LLM, no latency, no per-call cost.

2. Post Optimizer — score the post

This is my favorite. Paste a caption and a target platform, and it scores the post out of 100 with actionable feedback.

POST /post/analyze
{ "text": "I went to the gym today.", "platform": "instagram" }

{
  "score": 28,
  "rating": "poor",
  "suggestions": [
    "A bit short — aim for 70-150 characters.",
    "Add 5-15 relevant hashtags to boost reach.",
    "Add 1-3 emojis to make the post more eye-catching.",
    "Add a call-to-action (e.g. \"Save this\", \"Comment below\").",
    "Try asking a question to spark comments."
  ]
}

A strong post scores 90+. The rules (ideal length, hashtag range) adapt per platform — Instagram, X, TikTok, LinkedIn and Facebook each have different sweet spots.

How the scoring works under the hood — a set of weighted checks:

// length, hashtags, emojis, CTA, engagement-question — each weighted
const earned = checks.reduce(
  (s, c) => s + c.weight * (c.status === 'pass' ? 1 : c.status === 'warn' ? 0.5 : 0), 0
);
const score = Math.round((earned / total) * 100);

3. Username Generator — brand the account

Completes the username flow: generate ideas, then check availability with the existing /username/check endpoint.

GET /username/generate?keywords=coffee,shop&style=pro

{
  "suggestions": ["getcoffee", "coffeeco", "coffee_hq", "coffeestudio", "coffeelabs", "teamcoffee"],
  "tip": "Check availability with GET /username/check?username=<name>"
}

Four styles: clean, fun, pro, short.

The takeaway

The API is now 16 endpoints — a full content workflow: generate → optimize → brand. Everything is algorithmic (no LLM cost), returns clean JSON, and runs on free-tier serverless infra (Vercel + Upstash).

Try it free (no credit card):
👉 Social Media Toolkit on RapidAPI

What tool should I add next? I'm taking requests in the comments 👇

I built an all-in-one Social Media Toolkit API — 8 tools in one endpoint set

Manal166 — Sat, 06 Jun 2026 10:35:38 +0000

TL;DR: I bundled 8 commonly-needed social media utilities into a single API — username availability, hashtag generation, engagement rate, best time to post, competitor analysis, bio generation, profile validation and link shortening. It's live on RapidAPI with a free tier. Here's how I built it and how you can use it.

The problem

Every time I worked on a social-media-related side project, I needed the same small utilities:

Is this username taken on Instagram / GitHub / TikTok?
What hashtags should I suggest for this topic?
What's the engagement rate of this account?
When is the best time to post?

Each one is a tiny problem, but wiring them up separately (and legally, without scraping) is annoying. So I built Social Media Toolkit — one API that does all of it.

What's inside

Endpoint	What it does
`GET /username/check`	Username availability across 15+ platforms
`GET /hashtags/generate`	Relevant hashtags for any topic
`GET /engagement/calculate`	Engagement rate + rating
`GET /besttime`	Best posting times per platform & day
`POST /competitor/analyze`	Compare accounts with leaderboards
`GET /bio/generate`	Ready-to-use bios from keywords
`GET /profile/validate`	Detect platform & handle from a URL
`POST /shorten`	Short links with click analytics

Everything returns clean JSON and is 100% legal — no Terms-violating scraping.

Quick example

Generating hashtags is a single GET request:

curl --request GET \
  --url 'https://social-media-toolkit1.p.rapidapi.com/hashtags/generate?topic=fitness&count=10' \
  --header 'X-RapidAPI-Key: YOUR_KEY' \
  --header 'X-RapidAPI-Host: social-media-toolkit1.p.rapidapi.com'

Response:

{
  "topic": "fitness",
  "count": 10,
  "hashtags": ["#fitness", "#workout", "#gym", "#health", "#fitlife", "..."],
  "string": "#fitness #workout #gym #health #fitlife ..."
}

Or calculate engagement rate:

GET /engagement/calculate?followers=10000&likes=450&comments=30

{
  "followers": 10000,
  "engagement_rate_percent": 4.8,
  "rating": "high"
}

The tech stack (and why)

Node.js + Express — simple, well-supported, fast to ship.
Vercel (serverless) — free, no credit card, public HTTPS URL.
Upstash Redis — free, serverless, persistent storage for the link shortener (Vercel's filesystem is read-only).
RapidAPI — handles billing, keys, rate limiting and the marketplace.

One nice detail: the storage layer auto-selects its backend. Locally it uses Node's built-in node:sqlite; in production it uses Upstash Redis when the env vars are present — so the same code runs offline and in the cloud.

const useRedis =
  !!process.env.UPSTASH_REDIS_REST_URL && !!process.env.UPSTASH_REDIS_REST_TOKEN;

let backend;
if (useRedis) {
  ({ redisBackend: backend } = await import('./stores/redis.js'));
} else {
  ({ sqliteBackend: backend } = await import('./stores/sqlite.js'));
}

Securing it

Because the API runs on a public URL, I lock it to RapidAPI traffic with a proxy-secret check, so nobody can bypass billing by hitting the URL directly:

export function rapidApiAuth(req, res, next) {
  if (process.env.ENFORCE_PROXY_SECRET !== 'true') return next();
  const provided = req.header('X-RapidAPI-Proxy-Secret');
  if (provided !== process.env.RAPIDAPI_PROXY_SECRET) {
    return res.status(403).json({ error: 'Forbidden' });
  }
  next();
}

Try it

It's live with a free tier (500 requests/month) — no credit card to start:

👉 Social Media Toolkit on RapidAPI

I'd genuinely love feedback — what tool would you add next? Drop a comment 👇