Why a VAT Validation MCP Server Uses Two Separate Tools Instead of One

Developer building vatnode-mcp, the official MCP server for VAT-validation SaaS vatnode, chose to split VAT validation into two distinct tools: check_vat_format and validate_vat_number. The first performs an instant, free, offline regex check to confirm whether a VAT number matches the expected pattern for a given country. The second makes a live network call to the EU's VIES registry to verify whether the number is actually registered and retrieve the associated company name. Combining both into one tool would force every caller to bear the latency and failure risks of a VIES lookup even when only a quick format check is needed. The design reflects a broader API principle: tools with opposite cost and reliability profiles serve different use cases and should remain separate to avoid silently degrading the quality of answers.