W System / E-invoicing API for EU mandates, built for SaaS builders and AI apps

E-invoicing API for EU mandates, built for SaaS builders and AI apps

Short answer: If your app creates invoices for EU businesses, the law is changing under you: Belgium requires Peppol B2B e-invoices since 1 January 2026, Poland's KSeF is mandatory since February/April 2026, every French business must receive e-invoices since 1 September 2026, and German businesses must issue them from 2027. W System gives you one call, POST https://api.wsystem.dev/einvoice/send, that verifies the buyer's VAT number (VIES) and screens sanctions lists, builds an EN 16931 UBL invoice from simple JSON, validates it against the official rules, looks up how the buyer can receive it (Peppol Directory, country mandate, French directory) and returns an Ed25519-signed evidence receipt. Today this runs in sandbox mode: every step is real except transmission, which is simulated and clearly labelled. Live Peppol sending through a certified access-point partner is next. Get early access: get an API key or email [email protected] with your countries and monthly volume.

Today /einvoice/send runs in sandbox mode: every step is real except transmission, which is simulated. Live Peppol delivery via a certified access-point partner is next.

Key facts

What is live today: /einvoice/validate (EN 16931 + XRechnung rules; UBL, CII, ZUGFeRD/Factur-X PDF), /einvoice/create (JSON to UBL: en16931, xrechnung, peppol-bis3 structure), /einvoice/route (VIES + Peppol Directory + mandate), /kyb/check, /ddreport, and /einvoice/send in sandbox mode (mock transport, nothing is transmitted). MCP tools at https://api.wsystem.dev/mcp/.
What is not live yet: real transmission over Peppol, KSeF submission, delivery to a French accredited platform (PA), receiving invoices, webhooks, Peppol BIS 3 specific rules (PEPPOL-EN16931-*). mode=live returns HTTP 501 until a partner transport is configured and tested. We are not a certified Peppol Access Point or French PA ourselves; live sending will go through a certified partner.
Belgium: structured B2B e-invoicing via Peppol (BIS Billing 3.0) mandatory between Belgian VAT-registered businesses since 1 January 2026; penalties apply since 1 April 2026. Source: FPS Finance.
Poland: KSeF (national clearance, FA(3) XML) mandatory for large taxpayers since 1 February 2026 and for other VAT taxpayers since 1 April 2026; micro taxpayers from 1 January 2027. Sources: Ministry of Finance, ksef.podatki.gov.pl.
France: every business must be able to receive e-invoices since 1 September 2026 (large and mid-size companies also issue); SMEs and micro-businesses must issue from 1 September 2027, through an accredited platform (plateforme agréée). Source: impots.gouv.fr.
Germany: all businesses must be able to receive EN 16931 e-invoices since 1 January 2025; issuing is mandatory from 1 January 2027 for prior-year turnover above EUR 800,000 and from 1 January 2028 for everyone (XRechnung or ZUGFeRD/Factur-X). Source: Federal Ministry of Finance FAQ.
EU (ViDA): e-invoicing and digital reporting for intra-EU B2B from 1 July 2030. Source: European Commission.
Evidence receipt: a compact JWS (EdDSA/Ed25519) over the SHA-256 of the exact XML, the VIES result (with consultation number when available), the validation summary, the route and the transport result. Public key: /einvoice/evidence-key. In sandbox mode the receipt says sandbox: true and does not prove delivery.
Built for AI-built apps and agents: one JSON shape, plain-English errors with official rule IDs, an MCP tool (send_einvoice_sandbox) and pay-per-call via x402 or a monthly API key.

Examples

Sandbox send (nothing is transmitted)

curl -s https://api.wsystem.dev/einvoice/sample > invoice.json
curl -X POST https://api.wsystem.dev/einvoice/send \
  -H 'Content-Type: application/json' \
  -d "{\"mode\":\"sandbox\",\"transport\":\"mock\",\"invoice\":$(cat invoice.json)}"

Response (shortened)

{"status": "simulated", "sandbox": true,
 "notice": "SANDBOX: nothing was transmitted ...",
 "steps": [{"step": "verify_buyer_vat"}, {"step": "screen_buyer_sanctions"}, {"step": "create_and_validate"}, {"step": "route_lookup"}, {"step": "transmit", "result": "simulated"}],
 "invoice": {"number": "INV-2026-001", "sha256": "..."},
 "evidence": {"jws": "eyJhbGciOiJFZERTQSIs...", "alg": "EdDSA", "kid": "wsys-ev-2026-10"}}

Can I e-invoice this company?

curl 'https://api.wsystem.dev/einvoice/route?id=BE0403170701'

Pricing

Channel	Price
Free tier	20 calls/day per IP across all endpoints, no key
x402 POST /einvoice/send (sandbox)	$0.08 USDC per call (same as create)
API key plans	Starter EUR 19/month (5,000 units), Pro EUR 49/month (25,000 units); /einvoice/send uses 8 units
Live sending (planned, not yet available)	Target per-invoice pricing will be published before launch; early-access accounts get it first

Questions and answers

Can I send real e-invoices today?

No. Verification, creation, validation and routing are live; transmission is sandbox only. We will announce live Peppol sending on this page and in llms.txt when it works end to end.

How do I get early access?

Get an API key from the pricing section on the home page (it also works for every live endpoint today), or email [email protected] with the countries and monthly invoice volume you need. Early-access users are the first onto live Peppol sending.

Which countries will live sending cover first?

Peppol first (Belgium and other Peppol countries), then Poland KSeF and France through partners. The order depends on partner onboarding; this page will say what is live.

Is this tax advice?

No. It is technical processing against official rule sets and directories.

Do you store invoices?

The sandbox flow does not store invoice content; it returns the XML and receipt to you. Only call counters are kept.

Facts and competitor details checked 2026-10-17. W System is the maker of this product. Not affiliated with the European Commission. Not legal or tax advice.