Taxid.dev VS Diffyn

Taxid.dev's answer

TaxID is the only VAT validation API that combines four things at once:

• A truly free forever plan (100 validations/month, no credit card)
• Sub-10ms cached responses via Redis (24h cache on valid lookups)
• Coverage across 31 countries from a single endpoint — 27 EU member states via VIES, plus UK (HMRC), Switzerland, Norway and Australia (ABR)
• Stripe-style structured error codes you can branch logic on (vatinvalid, serviceunavailable, countrynotsupported)

Other providers either charge from the first call, only cover EU VIES, or return SOAP/XML you need to parse. TaxID is the thin REST wrapper that just works.

Diffyn's answer:

Addresses workflow and change management on LLM prompts, provide teams with traceability and visualization of tests across multiple models, provide deeper understading into efficiency of these prompts.

Taxid.dev's answer

Three reasons:

1. Developer-first DX. REST, JSON, OpenAPI spec, Stripe-style error codes, country-specific format validation before hitting VIES (so malformed numbers fail instantly without consuming quota). Most competitors are SOAP wrappers with cryptic errors.

2. Real free tier. 100 validations per month, no credit card. Vatstack, Vatlayer and Avalara either require a card upfront or have hard limits that block real evaluation. With TaxID you can ship a side project to production on the free plan.

3. Extended coverage. Most VAT APIs stop at the EU. TaxID adds the UK (HMRC), Switzerland, Norway and Australia (ABR) — useful for any SaaS with global B2B customers.

Honest about limits: TaxID is not an enterprise compliance suite. If you need US sales tax nexus, full ERP integration or KYB beyond VAT, look at Avalara or Sovos. TaxID is for developers who need to validate a VAT number reliably inside a checkout or invoice flow.

Diffyn's answer:

Diffyn is the platform that specializes on both change management and multi-model analysis.

Taxid.dev's answer

• Hono on Cloudflare Workers (edge runtime, low cold start)
• Redis for 24h cache on valid VAT lookups
• VIES SOAP service (EU Commission) as upstream for all 27 EU member states
• HMRC API for UK VAT validation
• Australian Business Register (ABR) for Australian ABN validation
• TypeScript end to end, with zod for runtime schema validation
• OpenAPI 3.1 spec auto-generated from route handlers

Diffyn's answer:

React, Next.js, POSTGRESQL

Taxid.dev's answer

Developers building B2B SaaS or eCommerce products that need to validate company tax IDs as part of their billing flow.

Typical users: - SaaS founders integrating Stripe with EU VAT compliance (reverse charge mechanism) - Backend developers working on B2B checkouts in Node.js, Python, PHP or Go - Indie hackers shipping products to European customers who can't afford enterprise tax compliance tools - Accounting and ERP integration developers - Compliance and KYB workflow builders

The shared trait: they want a clean REST API with a free tier, not an enterprise sales call.

Diffyn's answer:

Professionals incorporating LLMs or AI tools in their workflow and wants to keep track of changes and test their prompts.

Taxid.dev's answer

TaxID was built after running into the same problem on three consecutive client projects: validating EU VAT numbers reliably.

The official EU source — VIES — is SOAP-based, frequently goes down without warning, has no caching layer, and returns errors like "MS_UNAVAILABLE" with no context. Every time, the workaround was the same: write a thin wrapper, add Redis cache, handle the downtime, parse the SOAP response into something usable.

Instead of writing it a fourth time, I built TaxID as a public API. The free tier exists because that's what I would have wanted on those projects — a way to evaluate the product without a sales cycle.

The product is intentionally small: one well-built endpoint, structured errors, fast cached responses. No tax calculation, no nexus tracking, no enterprise dashboard. Just the VIES wrapper VIES should have been.

Diffyn's answer:

I started working on Diffyn when I notice that prompting has become an essential part of work across many industries. While there are version control platofrms like github, they are not designed for just prompt management are can be overkill such applications, it is also not integrated natively with various LLMs and relevant tools for users to validate ideas and visualise results properly.