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Developer guides

VAT validation is the process of verifying that a business's VAT identification number is registered and active with the issuing tax authority. Inside the EU, validation runs against VIES (the VAT Information Exchange System maintained by the European Commission); the United Kingdom uses HMRC, Switzerland uses the BFS UID Register, Norway uses Brønnøysund, and Australia uses the ABR. Each system has different response shapes, rate limits, and downtime characteristics.

For developers building B2B billing, checkout, or compliance flows, getting VAT validation right matters for tax-exempt invoicing under the EU reverse charge mechanism, for OSS / IOSS reporting on cross-border digital sales, and for keeping consultation numbers on file as audit evidence. The guides below cover integration patterns, country-specific quirks, error handling, and how Avatcado compares to other APIs in the space.

How to Validate EU VAT Numbers Programmatically

Learn how to validate EU, UK, Swiss, Norwegian, and Australian VAT/GST numbers using a REST API. Covers VIES, HMRC, code examples in TypeScript and Python, and integration testing with test mode.

VIES API Guide: How to Use the EU VAT Validation Service

A developer's guide to the VIES SOAP API: how it works, its limitations, common error scenarios, and how to use a modern REST wrapper instead.

VAT Validation API Comparison: Avatcado vs VATstack vs vatlayer vs VATsense (2026)

An honest comparison of VAT validation APIs: pricing, features, DX, and SDK support across Avatcado, VATstack, vatlayer, VATsense, and vatapi.com.

How to Handle VAT Validation in Your SaaS Billing Flow

Learn how to integrate real-time VAT validation into your SaaS checkout flow. Covers reverse charge logic, Stripe integration, and storing validation proof.

EU VAT Reverse Charge: What Developers Need to Know

Understand the EU reverse charge mechanism in developer terms. When it applies, how to validate with consultation numbers, and what your code needs to handle.

HMRC VAT Check API: A Developer's Guide to UK VAT Validation

How to validate UK VAT numbers using the HMRC API. Covers OAuth 2.0 authentication, endpoint structure, common errors, and a simpler alternative.

How to Validate VAT Numbers in TypeScript

Validate EU, UK, Swiss, Norwegian, and Australian VAT/GST numbers in TypeScript with the @avatcado/node SDK. Covers error handling, batch validation, test mode, and framework integration.

VIES Downtime: Why It Happens and How to Handle It

Why VIES goes down, which EU countries are least reliable, and how to keep your VAT validation working during outages with caching and stale fallback.

Swiss VAT Number Validation API: CHE Format, UID Register, and Liechtenstein

How to validate Swiss and Liechtenstein VAT numbers using the BFS UID Register. Covers the CHE format, MWST/TVA/IVA suffixes, MOD11 checksum, and the difference between a valid UID and active VAT registration.

Norwegian VAT Number Validation API: MVA Format and Bronnysund Register

How to validate Norwegian VAT numbers (MVA) using the Bronnysund Register Centre API. Covers the organization number format, MOD11 checksum, and the difference between an existing org and active MVA registration.

Australian GST Validation API: ABN Format, ABR Lookup, and GST Registration

How to validate Australian ABNs and GST registration using the ABR Lookup service. Covers the ABN format, weighted checksum algorithm, GST registration status, and the JSONP response format.

How to Validate ABN and GST Numbers in Australia via API

A developer guide to validating Australian ABNs and GST registration numbers via API. Covers checkout integration, batch validation for vendor onboarding, and edge case handling.

VAT Validation for Mollie Merchants: How to Validate Customer VAT Numbers

Mollie does not validate customer VAT numbers. Learn how to add VAT validation to your Mollie checkout flow for B2B reverse charge compliance using Avatcado.

VAT Validation for Stripe Users: What Stripe Covers and Where You Need Avatcado

Stripe validates EU, UK, and AU tax IDs but skips Swiss, Norwegian, and 100+ other types. Learn where Stripe's validation falls short and how Avatcado fills the gaps.

EU VAT Reverse Charge: Why Validation is Required and How to Implement It

Since January 2020, a valid VAT number is legally required for the 0% reverse charge rate. Learn the law, the implementation, and how to stay compliant.

EU VAT Validation for US SaaS Companies: What You Need to Know

US SaaS companies selling B2B to EU customers can avoid charging VAT via the reverse charge, but must validate the buyer's VAT number. Here's how.

VAT Validation for Adyen Merchants: How to Handle B2B VAT Compliance

Adyen does not offer customer VAT validation. Learn how to add VAT number verification to your Adyen checkout for B2B reverse charge compliance.

Async VAT Validation: Webhooks, Batch Processing, and Background Validation

Learn how to validate VAT numbers asynchronously using webhooks and batch processing. Covers checkout latency, bulk revalidation, VIES downtime resilience, and webhook signature verification.

Validate VAT Numbers in Your CRM

How to add real-time VAT number validation to CRM account creation and lead qualification workflows. Covers Salesforce, HubSpot, and no-code automation tools.

Salesforce VAT Validation

How to validate VAT numbers inside Salesforce using Apex HTTP callouts. Covers Named Credentials, the Avatcado REST API, and writing the validated company name back to Account records.

VAT Validation with Zapier

How to validate VAT numbers in a Zapier workflow using the Webhooks by Zapier action and the Avatcado REST API. No code required.

VAT Validation with Make

How to validate VAT numbers in a Make scenario using the HTTP module and the Avatcado REST API. No code required.