JSON Validator
Check whether JSON is valid and find the exact line and column of any syntax error.
Regex Tester
Test JavaScript regular expressions against your text with highlighted matches, capture groups and a live replace preview.
How to use
- Enter a pattern without the surrounding slashes and choose flags.
- Paste test text. Matches are highlighted and listed with their groups.
- Optionally enter a replacement ($1, $) to preview the result.
What this tool does
Patterns run with your browser’s JavaScript regex engine in a separate Web Worker. If a pattern takes longer than two seconds, for example because of catastrophic backtracking, the worker is stopped and you get a warning instead of a frozen tab.
Tips
- PHP (PCRE), Python and JavaScript regex are similar but not identical; lookbehind and named groups vary.
- Nested quantifiers like (a+)+ can be extremely slow on non-matching input.
Frequently asked questions
Which regex flavour is this?
ECMAScript (JavaScript), as implemented by your browser. Most everyday syntax is shared with PHP's preg functions.
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