Every product & business code.
Checked in one click.
Free, deterministic tools for barcodes and classification codes — check digits, format conversion, validation. Instant results, no sign-up, no AI guesswork.
Free tools
GTIN / UPC / EAN Check Digit Calculator
Calculate or validate the check digit of GTIN-8, UPC-A, EAN-13 and GTIN-14 barcodes.
UPC ↔ EAN Converter
Convert UPC-A to EAN-13 (and back), and build GTIN-14 case codes with the right indicator digit.
ISBN-10 ↔ ISBN-13 Converter
Convert and validate ISBNs with the official check digit formulas. Perfect for book sellers.
Bulk Barcode Validator
Paste a list of GTIN/UPC/EAN codes and validate them all at once, with a per-row report.
NAICS & SIC Code Lookup
Type a business activity, get the right NAICS 2022 and SIC code — all 2,125 official entries.
SIC ↔ NAICS Crosswalk
Convert SIC codes to NAICS (and back) using the official Census concordance tables.
Guides
How to Find Your NAICS Code for SAM.gov
Choosing the right primary code, size standards, and the mistakes that delay registration.
HS vs HTS vs Schedule B Codes
The customs code pyramid explained, with one product followed through every system.
Fix "Invalid GTIN" Errors on Amazon
The four causes of GTIN rejections and the step-by-step fix for each.
Excel Removed My Leading Zeros
Why Excel breaks barcodes and four reliable ways to prevent or repair it.
How Check Digits Work
Mod-10 and Mod-97 explained with fully worked examples.
SIC vs NAICS Codes
History, structural differences, and how to convert between the two systems.
Need to classify or validate thousands of items?
The CodeClassify API does everything these tools do, programmatically: bulk validation, NAICS/SIC classification, HS code search. Free tier: 25 calls per month, then pay only for what you use.