Hex Color Code Regex

Validation

Regular expression

/^#?(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$/

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

#ff0066

Should not match

#ff00zz
not matching sample
#ff0066 invalid
#ff00zz#ff0066

Test cases

Input	Expected	Why it matters
`#ff0066`	Match	Representative valid input for this pattern.
`#ff00zz`	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.
`#ff0066 invalid`	No match	Common invalid or boundary input.
`#ff00zz#ff0066`	No match	Common invalid or boundary input.

JavaScript

const re = /^#?(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$/;
re.test(input);

Python

import re
bool(re.search(r"^#?(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$", text))

PHP

$ok = preg_match('/^#?(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$/', $value) === 1;

Java

Pattern pattern = Pattern.compile("^#?(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$");
pattern.matcher(value).find();

Go

re := regexp.MustCompile(`^#?(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$`)
ok := re.MatchString(value)

Notes and production use

Hex Color Code 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.

Hex Color Code