What is an example of a matching and non-matching string?

A valid matching string is "ghcr.io/org/service-app:v1.4.2". A non-matching string is "Invalid Image Name : With Spaces".

Is this regex safe from ReDoS (Catastrophic Backtracking)?

Yes, this pattern is optimized for linear execution time and safe for browser-side validation without locking up the UI thread.

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Docker Image Repository & Tag Name Regex

Q: What is the regex pattern for Docker Image Repository & Tag Name Regex?

The regular expression pattern is /^(?:(?=[^:\/]{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})?$/. Validates complete Docker image references including optional registry domain, namespace, image name, and tag.

Q: How do I test this regex in JavaScript and TypeScript?

Use regex.test(): const regex = /^(?:(?=[^:\/]{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 isValid = regex.test(inputString);

Validates complete Docker image references including optional registry domain, namespace, image name, and tag.

Regular Expression 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})?$/

Valid Match Example:

ghcr.io/org/service-app:v1.4.2

Invalid / Non-Match Example:

Invalid Image Name : With Spaces

Regex Syntax Breakdown & Explanation

•Matches optional registry host (e.g. registry.hub.docker.com:5000/)
•Matches multi-tier organization or username repositories
•Matches standard Docker tag with colon separator

Implementation in Popular Languages

JavaScript / TypeScript

const regex = /^(?:(?=[^:\/]{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 isValid = regex.test("ghcr.io/org/service-app:v1.4.2");
console.log(isValid); // true

Python (re)

import re

pattern = r"^(?:(?=[^:\/]{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})?$"
match = re.match(pattern, "ghcr.io/org/service-app:v1.4.2")
print(bool(match)) # True

Go (regexp)

package main
import (
  "fmt"
  "regexp"
)

func main() {
  re := regexp.MustCompile(`^(?:(?=[^:\/]{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})?$`)
  fmt.Println(re.MatchString("ghcr.io/org/service-app:v1.4.2"))
}

Frequently Asked Questions

Everything you need to know regarding specifications, syntax, and security best practices.

The regular expression pattern is /^(?:(?=[^:\/]{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})?$/. Validates complete Docker image references including optional registry domain, namespace, image name, and tag.