Docker Image Tag Regex for Python

What this pattern does

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

Python Implementation

# Docker Image Tag
# ReDoS-safe | RegexVault — Dev & Systems > Docker

import re

docker_image_tag_pattern = re.compile(r'^[a-zA-Z0-9][a-zA-Z0-9._\-]{0,127}$')

def validate_docker_image_tag(value: str) -> bool:
    return bool(docker_image_tag_pattern.fullmatch(value))

# Example
print(validate_docker_image_tag("latest"))  # 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 Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. 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.