W System / Guides

Guides and free tools

E-invoicing deadlines by country, free checkers, and the standalone VAT, EORI, sanctions and company-data APIs. Building invoicing or ERP software for many companies? Start with W System for platforms.

E-invoicing by country

E-invoicing API guides

• E-invoicing API for EU mandates (BE, PL, FR, DE)
• EU e-invoice API: validate, create and route EN 16931 invoices
• Read incoming XRechnung / ZUGFeRD / Factur-X invoices as JSON
• Factur-X / ZUGFeRD EXTENDED validation: why EN 16931 validators flag CII-SR and CII-DT rules
• EN 16931 and XRechnung validation rules: every rule ID explained (BR-CO-16, BR-S-08, BR-DE-15 …)
• Peppol participant lookup in 2026: OpenPeppol SML, SMP and a Python example
• Peppol participant identifier schemes: the ICD code list (0208, 9925, 9930, 0088 …)
• Check every e-invoice before it's sent

Free tools

• E-invoice validator
• Peppol ID lookup
• Bulk VAT checker for CSV files
• VIES status
• EORI lookup
• VIES API alternatives compared

VAT, EORI, sanctions and KYB APIs

• EU VAT number validation API (VIES)
• EU VAT validation guide
• VIES is down: handling MS_UNAVAILABLE and timeouts
• VIES error codes explained: MS_UNAVAILABLE, MS_MAX_CONCURRENT_REQ, TIMEOUT and more
• EORI number check API (EU, official EOS)
• Sanctions screening API (EU, UN, OFAC SDN, UK)
• European company registry API
• One-call KYB check for EU companies
• EU tenders (TED) search API and alerts

Plugins, MCP, x402 and the blog

• WooCommerce EU VAT number validation (free plugin)
• Shopware 6 EU VAT ID check with VIES (free plugin)
• MCP server for EU VAT, EORI, company registry and sanctions
• VAT number checker MCP for Claude: connect in Claude.ai, Claude Desktop and Claude Code
• x402: pay per call
• x402 API VAT validation for AI agents
• All articles on the W System blog