EasyText Processing3 min read

Mention Handle Regex

Validates a social-media style @mention handle: an @ symbol followed by 1 to 15 letters, digits, or underscores, matching common username length limits.

#mention#handle#username#social-media#text-processing#validation

Regex Pattern

^@[A-Za-z0-9_]{1,15}$

Pattern Breakdown

Hover over a token to see what it does.

^@[A-Za-z0-9_]{1,15}$

Token	Meaning
^	Anchors the match to the start of the string
@	Literal at-sign that begins every mention handle
[A-Za-z0-9_]	Character class allowing letters, digits, and underscores
{1,15}	Requires between 1 and 15 of the allowed characters, mirroring common platform handle-length limits
$	Anchors the match to the end of the string

Detailed Explanation

What it does

This pattern checks that a string is a single, complete @mention handle: an @ symbol followed by 1 to 15 alphanumeric or underscore characters, with nothing else before or after.

Why it works

The `{1,15}` bound directly encodes the maximum handle length used by several major social platforms, so both too-short (bare @) and too-long handles are rejected in one quantifier. Restricting the body to `[A-Za-z0-9_]` excludes spaces, punctuation, and hyphens, which keeps the handle a single unbroken token, and the `^`/`$` anchors ensure the entire input is the handle rather than a mention embedded inside a longer string.

Common use cases

Validating a single @mention entered into a compose box's tag-a-user field
Checking that autocomplete or lookup input for user handles is well-formed before hitting an API
Filtering a list of extracted mentions to discard malformed or over-length entries
Server-side validation of handles submitted via a public API before database lookup

Edge cases

A bare @ with nothing after it is correctly rejected as an empty handle
Handles at exactly the 15-character boundary, like @exactly_fifteen, are matched, while 16 characters is rejected
Handles containing a leading digit, like @1username, are accepted since digits are allowed anywhere in the body
Handles with a dot or hyphen, common on some platforms for display names, are rejected since only letters, digits, and underscores are permitted

Limitations

Does not extract multiple @mentions from a larger block of free text; use a global, unanchored variant for that
The 15-character limit is specific to certain platforms and may need adjusting for others with different handle-length rules
Does not verify that the mentioned user account actually exists
Does not support Unicode letters for platforms that allow non-ASCII characters in handles

Interactive Tester

Edit the pattern or text below — matching runs live in your browser.

Open in Playground →

@jack @dev_user01 @a

3 matches

Test Cases

Editable — add your own inputs to see if they pass.

Input	Expected	Result
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Language Variants

Production-ready examples in 12 languages.

const mentionRegex = /^@[A-Za-z0-9_]{1,15}$/;
console.log(mentionRegex.test('@jack')); // true

Common Mistakes

Using an unbounded `+` for the handle body, which allows arbitrarily long strings that violate real platform limits

Fix: Bound the quantifier explicitly, such as `{1,15}`, to match the target platform's actual handle-length rule

Allowing hyphens or dots in the handle body, which many mention systems disallow

Fix: Restrict the character class to `[A-Za-z0-9_]` unless the target platform explicitly permits other characters

Trying to use this anchored single-handle pattern to pull every mention out of a block of text

Fix: Remove the `^`/`$` anchors and add the `g` flag to find all `@handle` occurrences within free-form text

Performance Notes

The bounded `{1,15}` quantifier keeps the maximum match length small and predictable, avoiding any risk of runaway backtracking
Anchoring with `^` and `$` allows the engine to fail fast on strings that do not begin with @
For bulk validation of many handles, compile the regex once and reuse the same instance across calls

Browser Compatibility

Engine	Supported	Notes
Chrome	Yes	—
Firefox	Yes	—
Safari	Yes	—
Edge	Yes	—
Node.js	Yes	—

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