Regex Tester Online
Type a regular expression to see every match in your text, each numbered and named group in its own column, a replace preview and the pattern explained in plain words. Load a log or data file to test on real text.
Regex Preview & Regex Tester for VS Code and Cursor, free
- A Test regex link above the regexes in your code, in 10 languages, with string escapes undone first.
- Flavors: JavaScript, Python, Java, .NET, Go/Rust (RE2) and PCRE, with a note for syntax that works differently in the one you pick.
- A railroad diagram of the pattern (export as SVG or PNG) and Copy as JavaScript, Python, Java, Go, C#, PHP or Rust code.
Optional Zovo Pro, USD 19 once: extract matches from files to CSV, and check the regexes of a workspace for catastrophic backtracking. 3 free tries for each.
Flags: g all matches, i ignore case, m ^ and $ at each line, s dot matches newlines, u Unicode, v Unicode sets, y sticky. Examples:
Or drop a text file anywhere on this page. Files up to 20 MB.
Matches
Groups
Replace
Explain
Open this in VS Code or Cursor
The free Regex Preview & Regex Tester extension puts a Test regex link above each regex in your JavaScript, TypeScript, Python, Go, Rust, Java, Kotlin, C#, PHP and Ruby code. It tests the pattern on your own text beside the editor, with groups, a replace preview in the flavor's own syntax, a railroad diagram and notes on syntax that works differently in your language.
Free, MIT license. About Regex Preview & Regex Tester for VS Code.
Zovo Pro
Extract matches to CSV and check regexes for catastrophic backtracking. Zovo Pro, USD 19 once.
In the Regex Preview & Regex Tester extension, Zovo Pro runs a regex over a log file or a whole folder and saves every match as a CSV row with one column per group (up to 1,000,000 rows), and checks every regex in your workspace for catastrophic backtracking, with the input that proves it. Each Pro tool works 3 times for free. One payment covers the Pro tools in 22 Zovo extensions. Everything that is free stays free.
After a card payment you get a key on the page. With GitHub Sponsors you sign in from the extension. Details on the Zovo Pro page.
Related tools
- JavaScript Playground & TypeScript Scratchpad. Shows the value of each line of JavaScript or TypeScript as you type.
- Large JSON Viewer & JSON Tree. Browses big JSON files as a searchable tree in VS Code.
- SQL Formatter. Formats SQL in VS Code, also on save.
- SARIF Viewer Online, free in your browser.
Questions
Is my text uploaded anywhere?
No. The page tests the pattern inside this tab, and a file you load is read with the File API. Its Content Security Policy sets connect-src to none, so the page cannot send your text anywhere. Open the Network tab of your browser tools and you will see no request while you test.
Which regex flavor does it use?
JavaScript, the engine built into your browser, with the flags d, g, i, m, s, u, v and y, named groups, lookbehind and Unicode property escapes. Python, Java, .NET, Go and PCRE differ in places, for example in lookbehind and possessive quantifiers. The Regex Preview & Regex Tester extension for VS Code lists those differences for the flavor you pick.
How do the groups and replace work?
Each match is a row, and each group in ( ) is a column, numbered in the order its ( appears. Named groups (?<name>...) show their name too, and a dash marks a group that did not take part in that match. In the replace box, $1 or $<name> puts a group back and $& the whole match, as in String.replace.
What if my pattern hangs?
The pattern runs in a background worker. If it takes more than 2 seconds, the page stops it and says so, so the tab never freezes. That is often a sign of catastrophic backtracking, such as (a+)+ on a long line with no match.
How much text can I test?
Files up to 20 MB. Matches are counted in the whole text, the table lists the first 5,000, and the highlight view shows the first 400,000 characters.
Does it work offline?
Yes. After the first visit the page keeps a copy of its own files, so it works with no connection.
What is free and what is Zovo Pro?
Everything on this page is free. In the VS Code extension, testing regexes, groups, replace, the railroad diagram, flavors and Copy as code are free too. Extracting matches from files to CSV and the catastrophic backtracking check are Zovo Pro, with 3 free tries each. One USD 19 payment covers the Pro tools in every Zovo extension.