Docker Image Tag Regex

Developer

Regular expression

/^[a-z0-9]+(?:[._/-][a-z0-9]+)*:[\w][\w.-]{0,127}$/

Pattern breakdown

Part	Meaning
`Anchor or context`	Use anchors when you need whole-string validation.
`Main token`	The core token sequence describes the accepted text shape.
`Character class`	Character classes limit which characters are valid.
`Quantifier`	Quantifiers control how many characters or groups are accepted.
`Flags`	Use language-specific flags such as i, m, or u only when needed.

Should match

toolumina/app:v1.2.3
example/app:v1.2.3

Should not match

Toolumina:latest
not matching sample
toolumina/app:v1.2.3 invalid
Toolumina:latesttoolumina/app:v1.2.3

Test cases

Input	Expected	Why it matters
`toolumina/app:v1.2.3`	Match	Representative valid input for this pattern.
`example/app:v1.2.3`	Match	Representative valid input for this pattern.
`Toolumina:latest`	No match	Common invalid or boundary input.
`(empty string)`	No match	Common invalid or boundary input.
`not matching sample`	No match	Common invalid or boundary input.
`toolumina/app:v1.2.3 invalid`	No match	Common invalid or boundary input.
`Toolumina:latesttoolumina/app:v1.2.3`	No match	Common invalid or boundary input.

JavaScript

const re = /^[a-z0-9]+(?:[._/-][a-z0-9]+)*:[\w][\w.-]{0,127}$/;
re.test(input);

Python

import re
bool(re.search(r"^[a-z0-9]+(?:[._/-][a-z0-9]+)*:[\w][\w.-]{0,127}$", text))

PHP

$ok = preg_match('/^[a-z0-9]+(?:[._\/-][a-z0-9]+)*:[\w][\w.-]{0,127}$/', $value) === 1;

Java

Pattern pattern = Pattern.compile("^[a-z0-9]+(?:[._/-][a-z0-9]+)*:[\\w][\\w.-]{0,127}$");
pattern.matcher(value).find();

Go

re := regexp.MustCompile(`^[a-z0-9]+(?:[._/-][a-z0-9]+)*:[\w][\w.-]{0,127}$`)
ok := re.MatchString(value)

Notes and production use

Docker Image Tag regex is useful as a practical starting point. Test it against your real input, avoid using it as the only security control, and prefer a parser when the format has complex grammar.

Performance tip: avoid running complex regular expressions repeatedly on very large untrusted strings without limits. Prefer anchored validation patterns, cap input length before matching, and use a parser when the target format has nested grammar.

Docker Image Tag