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simple-gtin-validator

Lightweight PHP library for validating GTIN (Global Trade Item Number) values and generating check digits.

GTIN is the umbrella format behind common barcode identifiers such as GTIN-8, UPC, EAN, and GTIN-14. This package normalizes the input, applies prefix filtering, and verifies the checksum used by the GTIN standard.

Contents

• Requirements
• Installation
• What the library does
• Quick start
• Working flow
• API reference
• Usage examples
• Prefix filtering
• Development workflow
• Limitations
• License
• Credits

Requirements

• PHP 7.4 or later
• Composer for installation and autoloading

Installation

Install the package with Composer:

Then load Composer's autoloader in your project:

What the library does

The GtinValidator class provides two public operations:

• isValidGtin($code) validates a GTIN-style value
• addCheckDigit($code) appends a GTIN check digit to an incomplete code

Supported GTIN lengths for validation:

• GTIN-8
• GTIN-12
• GTIN-13
• GTIN-14

Accepted input styles:

• Numeric strings such as '036000291452'
• Strings containing hyphens such as '978-0-552-13326-5'
• Numeric values such as 884571375091

Inputs are normalized before validation: numeric values are cast to strings, and hyphens are removed from string inputs.

Quick start

Working flow

Validation flow

When you call isValidGtin($code), the validator works in this order:

1. Normalize the input
   • Numeric values are converted to strings
   • String inputs are trimmed and hyphens are removed
2. Check the prefix
   • The validator rejects codes that begin with configured restricted prefixes
3. Validate format
   • The code must be numeric
   • The length must be 8, 12, 13, or 14 digits
4. Verify the check digit
   • The value is left-padded to 14 digits
   • The GTIN checksum is calculated and compared with the last digit

Check digit generation flow

When you call addCheckDigit($code), the validator:

1. Normalizes the input
2. Left-pads the value to 13 digits
3. Calculates the GTIN checksum
4. Returns the normalized value with the new check digit appended

This means short inputs are padded with leading zeroes before the check digit is generated.

API reference

isValidGtin($code): bool

Validates a GTIN code after normalization, prefix checks, and checksum verification.

Parameters

• $code: string or numeric scalar input (other types are not supported)

Returns

• true when the code passes prefix, length, numeric, and checksum validation
• false when the code is not acceptable after normalization, prefix filtering, and checksum verification

Throws

• An exception or fatal error if $code is neither a string nor a numeric value (this occurs during input normalization)

addCheckDigit($code): string

Generates and appends a GTIN check digit.

Parameters

• $code: string or numeric input representing a code without its final check digit

Returns

• A string with the computed check digit appended
• The input is padded on the left to 13 digits before the result is produced

Usage examples

Validate a standard GTIN

Validate input with hyphens

Hyphens are removed before validation, so this behaves the same as validating 9780552133265.

Understand a rejected code

This value is mathematically well-formed as an ISBN-style identifier, but the default prefix filter rejects 978 and 979.

Generate a check digit

Prefix filtering

The validator includes a public static prefix list that is checked before checksum validation:

By default, the list excludes these prefixes:

• 200-299
• 951
• 952
• 960-969
• 977
• 978-979
• 980
• 981-984
• 99

This is important because some values may have a valid checksum but still return false due to business rules in the prefix list.

If your use case needs different behavior, you can adjust the static list before validating:

Development workflow

This repository is intentionally minimal and currently does not include a dedicated automated test suite.

Useful local checks:

Typical workflow for local changes:

1. Install dependencies with Composer if needed
2. Update the source or documentation
3. Run composer validate --no-check-publish
4. Run php -l src/GtinValidator.php
5. Manually verify usage with a small PHP script or php -r

Limitations

• Input should be a string or numeric value
• Validation behavior depends on the configured prefix list, not only on checksum correctness
• addCheckDigit() left-pads inputs shorter than 13 digits before appending the final digit; inputs longer than 13 digits are not truncated, so the returned value can exceed 14 digits
• The package is focused on simple validation logic and does not provide barcode parsing or formatting helpers

License

Apache-2.0

Credits

• Original concept adapted from the Python version by charithe: https://github.com/charithe/gtin-validator
• GTIN and prefix reference material:
  • https://www.gs1.org/barcodes/technical/idkeys/gtin
  • https://www.gs1.org/standards/id-keys/company-prefix