JSON Field Name Regex

Extraction

Regular expression

/"([A-Za-z_][A-Za-z0-9_]*)"\s*:/

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

"email": "[email protected]"
"email": "[email protected]"
"email":"[email protected]"

Should not match

email = value
not matching sample
"email": "[email protected]" invalid
email = value"email": "[email protected]"

Test cases

Input	Expected	Why it matters
`"email": "[email protected]"`	Match	Representative valid input for this pattern.
`"email": "[email protected]"`	Match	Representative valid input for this pattern.
`"email":"[email protected]"`	Match	Representative valid input for this pattern.
`email = value`	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.
`"email": "[email protected]" invalid`	No match	Common invalid or boundary input.
`email = value"email": "[email protected]"`	No match	Common invalid or boundary input.

JavaScript

const re = /"([A-Za-z_][A-Za-z0-9_]*)"\s*:/;
re.test(input);

Python

import re
bool(re.search(r"\"([A-Za-z_][A-Za-z0-9_]*)\"\s*:", text))

PHP

$ok = preg_match('/"([A-Za-z_][A-Za-z0-9_]*)"\s*:/', $value) === 1;

Java

Pattern pattern = Pattern.compile("\"([A-Za-z_][A-Za-z0-9_]*)\"\\s*:");
pattern.matcher(value).find();

Go

re := regexp.MustCompile(`"([A-Za-z_][A-Za-z0-9_]*)"\s*:`)
ok := re.MatchString(value)

Notes and production use

JSON Field Name 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.

JSON Field Name