VAT Number Format Checker

WHAT IT DOES

Automatically detects and validates VAT (Value Added Tax) numbers on web pages using country-specific format patterns. The script scans page text for potential VAT numbers like GB123456789, DE123456789, or FR12345678901 and validates them against country-specific formats, length requirements, and check digit rules where applicable. The panel displays detected VAT numbers with their status (Valid/Invalid/Unknown), the country they appear to be from, and the country code. Valid numbers can be copied to clipboard with a single click, and results can be exported as text or JSON for audit and compliance purposes. Per-page validation results are saved per URL or custom identifier.

WHERE IT RUNS

Works on all websites (match pattern *://*/*), making it perfect for e-commerce platforms, invoicing systems, procurement portals, compliance dashboards, or any web page that displays or processes VAT numbers. Each page gets its own independent validation results set, allowing you to scan and track VAT numbers across multiple contexts. Results are saved per page identifier, ensuring continuity across sessions and page reloads.

HOW TO USE

Install the script and the VAT Number Format Checker appears in the panel. Click "Scan Page" to scan the current page for VAT numbers. The script detects potential VAT numbers and validates them against country-specific patterns. Each detected number is shown with a color-coded status indicator (green for valid, red for invalid), the country it appears to be from, and the country code. Click any valid VAT number to copy it to your clipboard. Use the export buttons to copy results as text or JSON for auditing. The script can auto-scan on page load if enabled. Customize the country patterns with your own regex rules for specialized formats.

REAL MECHANISM: COUNTRY-PATTERN-BASED VAT DETECTION WITH REGEX VALIDATION AND STRICTNESS LEVELS

This script uses a comprehensive VAT detection engine built around country-specific pattern definitions. The defaultPatterns array contains 28 EU country patterns with fields for country name, country code, regex pattern, and expected length. The extractVatNumbers() function first scans page text using a dynamic regex built from country codes (e.g., '(GB|DE|FR)...') to identify potential VAT numbers with country prefixes. Each candidate is then passed to validateVatNumber(), which tests it against all country patterns using new RegExp(pattern.pattern). The validation includes a length check that varies based on the user's selected strictness level: "loose" allows flexible length matching, "standard" permits ±2 character variance, and "strict" requires exact length match. The results are deduplicated using a Set to avoid duplicate entries. Each validated VAT number is stored with its id, number, country, code, valid status, and matches array. The render function displays results with a color-coded status dot, a click-to-copy VAT number element, a country badge, and a status label. Click-to-copy uses GM_setClipboard for reliable clipboard access. Settings (strictness, auto-scan) are persisted via GM_setValue. All operations are reactive, with automatic persistence through saveVatResults() and re-render.

THE PANEL

Drag the panel anywhere on screen by clicking and holding the header. It snaps to screen edges when released. Collapse it to a small bubble by clicking the minimize button, and expand it back by clicking the bubble. Resize the panel from any corner. Press Escape to close the configuration panel. Your position and size preferences are saved automatically per site.

PLEASE NOTE

This script requires the free BotGentz browser extension which provides the BGPanel framework and storage APIs. All data (detected VAT numbers, patterns, and page identifiers) is stored locally in your browser using GM_setValue and never sent anywhere. No analytics, no tracking, no external calls. The script only reads the current page content to detect VAT numbers and never accesses user data, passwords, or sensitive information. Validation is format-based only; the script does not perform live VAT number verification against government databases.