Docker Image Tag Regex for PHP

What this pattern does

This page provides a well-structured, multi-part regular expression for matching docker image tag, ported and verified for PHP. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your PHP project — whether you're validating in a Laravel validator, a WordPress plugin, or a standalone PHP script.

Php Implementation

<?php
// Docker Image Tag
// ReDoS-safe | RegexVault — Dev & Systems > Docker

define('DOCKER_IMAGE_TAG_PATTERN', '/^[a-zA-Z0-9][a-zA-Z0-9._\-]{0,127}$/');

function validate_docker_image_tag(string $input): bool {
    return (bool) preg_match(DOCKER_IMAGE_TAG_PATTERN, $input);
}

// Example
var_dump(validate_docker_image_tag("latest")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > Docker category and carries a ReDoS-safe certification. That matters for PHP developers because especially relevant in PHP where PCRE backtracking limits can trigger silent failures on malicious input. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Tags cannot start with a period or hyphen. 'latest' is the default tag if none is specified. Always pin to a digest (sha256:...) for reproducible deployments in production.