Docker Image Tag Validator

A Docker Image Tag Validator parses and validates Docker image reference strings. It extracts the registry hostname, namespace, repository name, tag, and digest. It checks that the tag meets length and character rules, that the digest follows the sha256:hex format, and produces a fully qualified reference.

This is useful when building CI/CD pipelines, writing deployment scripts, or debugging image pull issues. Invalid references often cause cryptic errors; this tool surfaces the exact problem.

The format is [registry_host/][namespace/]repository[:tag][@digest]. Registry defaults to docker.io. For Docker Hub official images, the namespace is library (e.g., nginx = docker.io/library/nginx). Tags are optional; if omitted, :latest is implied. Digests override tags when both are present for pull behavior.

Registry hostnames can contain ports (e.g., localhost:5000). Repository and namespace can use multiple path segments. The validator handles all these cases and reports each component with color coding.

Docker Hub: docker.io/namespace/repo:tag or just namespace/repo:tag. GHCR: ghcr.io/owner/repo:tag. AWS ECR: 123456789.dkr.ecr.us-east-1.amazonaws.com/repo:tag. GCR: gcr.io/project/repo:tag. Each registry may have slight variations. This tool provides preset examples for quick testing and validates the structure generically.