HTML Entity Regex

Replacement

Regular expression

/&(?:[a-zA-Z]+|#\d+|#x[0-9a-fA-F]+);/

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

Tom & Jerry
Tom&Jerry

Should not match

Tom & Jerry
not matching sample
Tom & Jerry invalid
Tom & JerryTom & Jerry

Test cases

Input	Expected	Why it matters
`Tom & Jerry`	Match	Representative valid input for this pattern.
`Tom&Jerry`	Match	Representative valid input for this pattern.
`Tom & Jerry`	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.
`Tom & Jerry invalid`	No match	Common invalid or boundary input.
`Tom & JerryTom & Jerry`	No match	Common invalid or boundary input.

JavaScript

const re = /&(?:[a-zA-Z]+|#\d+|#x[0-9a-fA-F]+);/;
re.test(input);

Python

import re
bool(re.search(r"&(?:[a-zA-Z]+|#\d+|#x[0-9a-fA-F]+);", text))

PHP

$ok = preg_match('/&(?:[a-zA-Z]+|#\d+|#x[0-9a-fA-F]+);/', $value) === 1;

Java

Pattern pattern = Pattern.compile("&(?:[a-zA-Z]+|#\\d+|#x[0-9a-fA-F]+);");
pattern.matcher(value).find();

Go

re := regexp.MustCompile(`&(?:[a-zA-Z]+|#\d+|#x[0-9a-fA-F]+);`)
ok := re.MatchString(value)

Notes and production use

HTML Entity 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.

HTML Entity