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Docker Image TagRegex — Pattern, Examples & Code

^(?:[a-z0-9]+(?:[._\-][a-z0-9]+)*\/)?[a-z0-9]+(?:[._\-][a-z0-9]+)*(?::[a-zA-Z0-9._\-]+)?$

What it matches / doesn't match

Matches ✅Does not match ❌
●nginx:latest●UPPERCASE/image
●my-org/api-server:1.2.3●image:tag:extra
●ubuntu:22.04●image with spaces

How it works

Matches Docker image references in name:tag format with an optional namespace prefix. Image names are lowercase alphanumeric with dots, underscores, or hyphens as separators. The tag (after :) allows alphanumeric, dots, underscores, and hyphens. Does not include registry host validation (e.g., ghcr.io/).

Code Usage

JavaScript

const regex = /^(?:[a-z0-9]+(?:[._\-][a-z0-9]+)*\/)?[a-z0-9]+(?:[._\-][a-z0-9]+)*(?::[a-zA-Z0-9._\-]+)?$/;
regex.test("nginx:latest"); // true

Python

import re
pattern = re.compile(r'^(?:[a-z0-9]+(?:[._\-][a-z0-9]+)*/)?[a-z0-9]+(?:[._\-][a-z0-9]+)*(?::[a-zA-Z0-9._\-]+)?$')
bool(pattern.match("nginx:latest"))  # True

Go

import "regexp"
r := regexp.MustCompile(`^(?:[a-z0-9]+(?:[._-][a-z0-9]+)*/)?[a-z0-9]+(?:[._-][a-z0-9]+)*(?::[a-zA-Z0-9._-]+)?$`)
r.MatchString("nginx:latest") // true

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FAQ

What does the Docker Image Tag regex pattern match?

Matches Docker image references in name:tag format with an optional namespace prefix. Image names are lowercase alphanumeric with dots, underscores, or hyphens as separators. The tag (after :) allows alphanumeric, dots, underscores, and hyphens. Does not include registry host validation (e.g., ghcr.io/).

How do I use the Docker Image Tag regex in JavaScript?

const regex = /^(?:[a-z0-9]+(?:[._\-][a-z0-9]+)*\/)?[a-z0-9]+(?:[._\-][a-z0-9]+)*(?::[a-zA-Z0-9._\-]+)?$/; regex.test("nginx:latest"); // true

Can I use the Docker Image Tag regex in Python?

Yes. import re pattern = re.compile(r'^(?:[a-z0-9]+(?:[._\-][a-z0-9]+)*/)?[a-z0-9]+(?:[._\-][a-z0-9]+)*(?::[a-zA-Z0-9._\-]+)?$') bool(pattern.match("nginx:latest")) # True