I'm not a developer. I shipped 4 APIs in two weeks. After 10 days: 10 subscribers, 43 calls, $0.

Luca Bianchini — Sat, 03 Oct 2026 10:59:03 +0000

Hi everybody.
My name is Luca and I'm not a developer. I shipped 4 APIs in two weeks. After 10 days I have 10 subscribers, 43 calls and $0.

My day job is in finance. I don't write code for a living. A few weeks ago I needed to validate EU VAT numbers for a side project, and I got angry at the SOAP/XML mess out there. So I did the thing everyone warns you about: I built my own APIs. Cloudflare Workers, a lot of AI help, and stubbornness.

Now there are four of them, all in the same boring niche (EU B2B compliance, the stuff invoicing software needs):

VAT validation against the official EU VIES service
Italian fiscal code decoder (checksum, omocodia, municipality lookup)
working days / public holidays calculator for IT, DE, FR, ES
IBAN validator, 73 countries

Total cost so far: 0€. Cloudflare free tier does everything. They live on RapidAPI with a free plan and two paid tiers.

Now the numbers, because nobody ever posts these:
10 subscribers. 43 total calls, and I'd guess 30 of those are my own tests. Revenue: $0. The 4 reviews on my listings? Friends. I asked them personally, one by one.

So yes, this is a "nobody cares about my product yet" post. But here's what surprised me, in both directions.

Things that broke (my favorites):

The ISTAT dataset stores the province as an object, so on launch day my beautiful API answered "birth_place: Roma ([object Object])". A stranger could have seen that on day one. Nobody did. Pure luck.
I once configured my top plan at $9 for 500,000 requests per month. I was about to sell half a million calls for the price of a coffee. Caught it before publishing. Barely.
A trailing slash in the base URL made my health check scream FAILURE for a whole day. One character.
I got permanently banned from a subreddit because my first post was "clearly written with AI". It was. This sentence you're reading is the revenge version: I'm writing it myself, badly, at night, after work.

Things I learned:
"Build it and they will come" is a lie told by people who already have an audience. Marketplaces don't show new APIs to anyone, because search is sorted by reviews and traffic... that you don't have yet. It's a locked door: you need traffic to get traffic. The only keys I found so far live outside the marketplace: answering real questions on Stack Overflow (with honest disclosure that the API is mine), one tutorial on Dev.to, and this post.

Where I am now: 4 APIs, 0 customers, 0 regrets. The product works. The distribution doesn't. Yet.

Questions for people who've been here:

Where do B2B developers actually discover APIs like these? RapidAPI search seems dead for newcomers. Is it Google? A newsletter? A Discord I don't know about?
Would you stay on the marketplace, or self-host with Stripe and eat the discovery problem yourself?
What's the one thing you'd fix in my positioning ("official sources, compliance-first, EU niche")?

I'll answer every comment. My English is not perfect and my energy today is even less, but I'll be here tomorrow morning with coffee.

Links in the first comment, so the post doesn't smell like an ad.

How to Onboard a EU B2B Customer in 15 Minutes: VAT, Fiscal Code and Working Days in One Flow

Luca Bianchini — Sat, 26 Sep 2026 11:59:50 +0000

The Problem

Every B2B SaaS serving EU customers faces the same onboarding friction:

Is this company's VAT number actually valid?
If I need to decode an Italian fiscal code, does it pass checksum?
When is this invoice actually due, considering weekends and national holidays?

Most teams end up stitching together 3-4 different sources, dealing with XML, SOAP, and inconsistent JSON formats. Today I'll show you a cleaner flow using 3 compliance-first APIs that I built specifically for this exact scenario.

Step 1: Validate the EU VAT number

Let's say a German company signs up: DE122268496. The official European Commission VIES service is the source of truth, but its native API can be... let's say "legacy-flavored."

With the EU VAT Validator API, it's a simple GET:


http
GET /check?vat=DE122268496
response
{
  "valid": true,
  "country": "DE",
  "vat_number": "122268496",
  "request_date": "2026-09-06",
  "company": {
    "name": "Registered Company Name",
    "address": "Registered Address"
  },
  "source": "VIES (European Commission)"
}

The API handles input normalization (spaces, dashes, lowercase) and gracefully reports errors. You get the official registered name and address — perfect for CRM enrichment.

Step 2: Decode the Italian fiscal code (for Italian customers)
If the same customer is Italian and provides their codice fiscale (e.g. RSSMRA85M01H501Q), we can extract much more than just validity:
GET /decode?cf=RSSMRA85M01H501Q
Response:
{
  "valid": true,
  "normalized": "RSSMRA85M01H501Q",
  "omocodia": false,
  "checks": { "format": true, "checksum": true, "date": true },
  "gender": "M",
  "birth_date": "1985-08-01",
  "birth_place_code": "H501",
  "birth_place": "Milano (MI)",
  "birth_country": "Italy",
  "source": "Official checksum algorithm + ISTAT municipal codes"
}
Key features:
Official checksum validation
Omocodia handling (letters replacing digits)
Birth date, gender, and municipality lookup from ISTAT cadastral codes
~8,000 Italian municipalities, cached for speed

Step 3: Compute the invoice due date in working days
Once the customer is validated, the next question is: when is this invoice due?
If payment terms are "30 working days from today", you can't just add 30 calendar days. You need to exclude weekends and national public holidays.

GET /workdays?from=2026-09-06&to=2026-10-31&country=IT
Response:
{
  "country": "IT",
  "from": "2026-09-06",
  "to": "2026-10-31",
  "total_days": 56,
  "weekend_days": 16,
  "holidays_on_weekdays": 2,
  "working_days": 38,
  "holidays_in_range": [
    {"date": "2026-11-01", "name": "All Saints' Day"}
  ],
  "note": "National public holidays only (local/patron saints not included)"
}
This API covers the 4 largest EU economies: Italy, Germany, France, and Spain. You can also fetch the full holiday list for any year with the /holidays endpoint.

Why This Flow Works
Single provider, consistent JSON: All 3 APIs use the same response format, error handling, and CORS policy. Integration is predictable.
Compliance-first sources: VAT from the European Commission, fiscal codes from official algorithms + ISTAT, working days from national calendars. No scraping, no legal gray areas.
Honest free tiers: Each API offers 100 free requests/month — enough for testing and small-scale usage. Scaling is predictable ($9 for 5,000, $29 for 50,000).
Same customer, same use case: These aren't random APIs thrown together. They're designed to be used in sequence by the same B2B customer.

How to Try It
All 3 APIs are live on RapidAPI with free tiers:
EU VAT Validator (VIES) → https://vies-vat-cheker.bianchini-luka.workers.dev
Italian Fiscal Code Decoder → https://cf-decoder.bianchini-luka.workers.dev
EU Working Days & Holidays → https://eu-workdays.bianchini-luka.workers.dev

Subscribe to the free plan on each, grab your API key, and start building. The documentation includes runnable examples in the console.

I built these APIs because I was tired of patching together brittle solutions for EU compliance. If you're building B2B software for European customers, I hope this flow saves you the same frustration.
Feel free to reach out via RapidAPI messaging if you have feedback, feature requests, or need custom integrations. Happy coding! 🚀

DEV Community: Luca Bianchini

I'm not a developer. I shipped 4 APIs in two weeks. After 10 days: 10 subscribers, 43 calls, $0.

How to Onboard a EU B2B Customer in 15 Minutes: VAT, Fiscal Code and Working Days in One Flow

The Problem

Step 1: Validate the EU VAT number