CheckDigitLab helps people check codes used in shops, shipping and finance. It serves barcode teams, analysts and developers who need check digits and a clear explanation of each result.
CheckDigitLab runs calculations in your browser as you type. There is no need to reload the page after each change. Barcode previews and step-by-step arithmetic let you check how the result was reached.
Who Runs CheckDigitLab
CheckDigitLab is an independent project owned and maintained by Shakeel Lodhi alongside a small team of web developers who build and maintain data tools for retail, e-commerce and logistics businesses. We work day to day with product catalogues, barcode feeds and shipping labels, which is where the need for a fast, transparent check digit tool came from.
Every algorithm on the site is implemented from the published specification, and the results are cross-checked against the worked examples in those specifications (for example the GS1 General Specifications sample GTINs and the ISO 13616 IBAN examples) before release. When a calculation question comes in through our contact page, it is answered by the same people who wrote the code.
What We Care About
- Zero Latency & Client-Side Execution: Every calculation (GS1 alternating 3-and-1 weights, Luhn double-add-double, ISO 7064 Modulo 97-10 big-integer divisions, and SEDOL/CUSIP character mappings) executes locally in your browser. Zero server roundtrips, zero latency.
- Real-Time Visual Intuition: Instead of merely displaying a lone result number, our engine renders live interactive multiplication pills, step totals, and a dynamic SVG barcode that highlights the check digit in real time.
- Absolute Privacy & Confidentiality: Your product SKU numbers, warehouse pallet SSCC tags, credit card prefixes, and financial identifiers belong exclusively to you. No input data is ever logged, transmitted, or stored on external servers.
- Broad Symbology & Standard Support: From retail point-of-sale (EAN-13, UPC-A, EAN-8) and logistics shipping containers (GTIN-14, SSCC-18, USPS) to financial identification (CUSIP, SEDOL, ISIN, IBAN), our system adheres strictly to published international specifications.
Mathematical Standards & Integrity
Our algorithms strictly conform to the authoritative industry specifications:
- GS1 General Specifications: Standard Modulo 10 calculation rules for EAN, UPC, GTIN, and SSCC barcodes.
- ISO/IEC 7812: Luhn algorithm standards utilized across international credit cards, debit cards, and cellular IMEI identifiers.
- ISO 7064 (MOD 97-10): Modulo 97 verification for international bank account numbers (IBAN).
- ANSI X9.6 & London Stock Exchange: Verification rules governing North American CUSIP and UK SEDOL securities.
The Technology Stack
CheckDigitLab is built with cutting-edge static architecture for rapid load times and peak reliability:
- Astro: Zero-overhead static architecture and lightning-fast edge delivery.
- Tailwind CSS: Highly responsive dark glassmorphism design system.
- TypeScript: Type-safe arithmetic routines ensuring bitwise and big-integer mathematical correctness.
- Native Scalable Vector Graphics (SVG): Dynamically rendered symbologies and barcode visualizations.
Get in Touch & Feedback
Have an idea for a feature, need support for a specialized regional barcode standard, or have feedback on our visualizer? We would love to hear from you. Visit our contact page to send feedback directly to our team.