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JavaScript Regex Tester — Live Match, Capture Groups, Replace Preview

Test JavaScript regex live — match highlighting, group capture, replace preview, flag toggles — browser-only

  • Runs locally
  • Category Text
  • Best for Removing repetitive cleanup work from everyday writing and operations.
//gi
Flags
Summary
Match count
2
First match at
8
Highlighted matches
Contact alice@example.com or bob@toolora.info anytime.
Capture groups (1st match)
$1 = "alice"
$2 = "example.com"

What this tool does

Free online regex tester for JavaScript flavour. Type a pattern and test text, see all matches highlighted in real time, with capture groups listed below. Supports all JS flags (g, i, m, s, u, y), replace preview (with $1 $2 backrefs), and shows match count + first match position. Catches invalid regex with the actual SyntaxError. 100% client-side.

Tool details

Input
Text + Structured content
The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output
Live result + Preview
The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy
Browser-side processing
The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share
Shareable URL state
Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget
Initial JS <= 8 KB
No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit
Text · Developer
Category and role tags drive related tools, internal links, and quick fit checks.

How to use

  1. 1. Input

    Paste or drop your content into the tool panel.

  2. 2. Process

    Click the button. All processing is local in your browser.

  3. 3. Copy / Download

    Copy the result or download to disk in one click.

How Regex Tester fits into your work

Use it to clean, compare, reshape, or extract plain text before it goes into a document, CMS, spreadsheet, or prompt.

Text jobs

  • Removing repetitive cleanup work from everyday writing and operations.
  • Making text easier to compare, paste, publish, or feed into another tool.
  • Working with content locally when the text is private or unfinished.

Text checks

  • Scan for unintended whitespace, duplicate lines, and lost punctuation.
  • For long text, test the first few lines before applying the whole change.
  • Copy the final output only after checking the preview.

Good next steps

These links move the current task into a more complete workflow.

  1. 1 Text Diff Compare two blocks of text — line-by-line additions, deletions, equal — colour highlighted, browser-only Open
  2. 2 JSON Formatter & Validator Format, validate, and minify JSON instantly — right in your browser. Open
  3. 3 Find and Replace Text Batch find-and-replace on big text — regex, $1 capture groups, whole-word, case toggle, multiple chained rules — runs entirely in your browser Open

Real-world use cases

  • Pull every email out of a pasted log dump

    Paste raw log text, type a pattern like [\w.]+@[\w.]+, flip on the g flag, and watch every email light up with a live match count. Copy the list straight from the match panel without writing a script.

  • Preview a backreference replace before committing it to code

    Test a capture-group pattern like (\d{4})-(\d{2})-(\d{2}) against sample dates, then type $3/$2/$1 in the replace field to see the rewritten output instantly. Confirm the backrefs land right before pasting the regex into your editor.

Common pitfalls

  • Typing \\d copied from a Java or Python string literal; write \d once here, the double backslash matches a literal backslash.

  • Forgetting the g flag, then wondering why only the first match highlights instead of all of them.

  • Expecting Python or PCRE syntax to work; this is the JavaScript RegExp engine, so named groups and old lookbehind forms may differ.

Privacy

Your pattern and test text run entirely in your browser through the native RegExp engine. Nothing is sent to a server, so you can safely test regexes against real log lines or private data.

FAQ

Tool combos

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Made by Toolora · 100% client-side · Updated 2026-07-02