Code & Markup · In-Browser Regular Expression Lab

Docker Image Tag Regex — Match Registry, Repository & Tag Syntax

Validates Docker image references such as repository/image:tag or standard official tags.

Pattern:

Regular Expression Pattern & Flags

Flags:

//none

Live Test String

Match Found

Load Sample:

Match Inspection & Details1 match

Match #1:nginx:alpine

Test Samples Verification Matrix

Expected Valid Samples (Should Match)

nginx:alpine Pass

ghcr.io/org/service:v1.2.3 Pass

node:20-slim Pass

redis:latest Pass

Expected Invalid Samples (Must Reject)

:latest Rejected (Pass)

repo:tag:extra Rejected (Pass)

-bad/name:tag Rejected (Pass)

Code Implementation Generator

// JavaScript / TypeScript (ES6+)
const pattern = /^(?:(?=[^:\/]{1,253})(?!-)[a-zA-Z0-9-]{1,63}(?<!-)(?:\.(?!-)[a-zA-Z0-9-]{1,63}(?<!-))*(?::[0-9]{1,5})?\/)?(?:[a-z0-9]+(?:(?:(?:[._]|__|[-]*)[a-z0-9]+)+)?\/)*[a-z0-9]+(?:(?:(?:[._]|__|[-]*)[a-z0-9]+)+)?(?::[\w][\w.-]{0,127})?$/;
const text = "nginx:alpine";

const isMatch = pattern.test(text);
console.log("Is Match:", isMatch);

if (isMatch) {
  const matches = text.match(pattern);
  console.log("Matches:", matches);
}

Regular Expression Token Breakdown

Validates Docker registry domain, namespace, repository name, and optional :tag component. Each component of the regular expression serves a distinct syntactical purpose as mapped below:

Token Pattern	Name / Component	Function & Rule
registry/	Optional Registry	Domain host like ghcr.io or docker.io.
repository	Repository path	Namespace and image name.
:[\w.-]{0,127}	Tag	Alphanumeric tag up to 128 characters.

Frequently Asked Questions

Is 'latest' matched automatically if omitted?

Docker CLI defaults to 'latest' if tag is omitted; this regex marks `:tag` optional.

Browse All 40 Patterns

Code & Markup

Semantic Version (SemVer 2.0)

Full SemVer 2.0.0 specification regex validating major, minor, patch, and optional pre-release/build tags.

/^(0|[1-9]\d*)\.(0|[1-9]\d*)\.(0|[1-9]\d*)(?:-((?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*)(?:\.(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?(?:\+([0-9a-zA-Z-]+(?:\.[0-9a-zA-Z-]+)*))?$/

Test regex

Code & Markup