How the pattern works
| Part | Meaning |
|---|---|
\B | Not a word boundary — the # must not follow a letter or digit, so issue#42 is skipped |
# | The hash sign |
[A-Za-z0-9_]+ | The tag: letters, digits and underscores |
Code examples
JavaScript
const matches = text.match(/\B#[A-Za-z0-9_]+/g) ?? [];Python
import re
matches = re.findall(r'\B#[A-Za-z0-9_]+', text)PHP
preg_match_all('/\B#[A-Za-z0-9_]+/', $text, $m);
$matches = $m[0];Notes and limitations
To support hashtags in any language, use \B#[\p{L}\p{N}_]+ with the u flag in JavaScript (Python needs the third-party regex module for \p{…}).
Regex TesterType a pattern and watch matches highlight live in your test text.
Open the tool Frequently asked questions
What is the regex to find hashtags?
/\B#[A-Za-z0-9_]+/g — it finds every match in a text. See the table above for what each part does.
Does it work in Python and PHP?
Yes — the code examples above use the same pattern with re in Python and preg functions in PHP.
How do I test this regex?
Click “Open in Regex Tester” — the pattern, flags and sample text load automatically, and matches highlight as you edit.