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// about this tool

Regex Tester Online

Updated 2026-08-19

Test regular expressions with live match highlighting, capture groups, and replace preview, right in your browser. Type a pattern and SnapTools highlights every match in your text as you type, breaks out captured groups, and previews substitutions. Nothing is uploaded — all matching runs locally, so it is safe for testing patterns against private or sensitive text.

Writing a regex blind and hoping it works is frustrating. The Regex Tester gives you instant feedback on what matches and what each group captures, so you can refine a validation rule, extract fields from logs, or debug a stubborn pattern in seconds.

// how to use

  1. 1 Type your regular expression in the pattern field and set flags such as g (global), i (case-insensitive), or m (multiline).
  2. 2 Paste the text to search in the input panel — matches highlight live as you type.
  3. 3 Inspect the captured groups below, and use the replace field to preview substitutions.

// examples

Match email addresses
Input
pattern: \w+@\w+\.\w+  text: contact ada@example.com or dev@test.org
Output
Matches: ada@example.com, dev@test.org (2 matches)
Capture groups
Input
pattern: (\d{4})-(\d{2})-(\d{2})  text: 2026-06-29
Output
Match: 2026-06-29 — group 1: 2026, group 2: 06, group 3: 29

// common uses

Building a validation pattern for forms Extracting fields from log lines Debugging a regex that misbehaves Previewing a regex-based replacement

// faq

Which regex flavor does it use?
It uses the JavaScript regular expression engine that runs in your browser, so syntax and behavior match what you would get in JavaScript code.
What do the flags do?
g finds all matches instead of just the first, i ignores case, m makes ^ and $ match line boundaries, and s lets the dot match newlines. Toggle them next to the pattern field.
Is my text or pattern uploaded anywhere?
No. Matching happens in your browser — nothing is uploaded, so it is safe for testing patterns against private or sensitive text.
What is the difference between this and find & replace?
Regex Tester is for building and debugging a pattern with live match and group feedback; Find & Replace applies a substitution across your whole text. Use the tester to perfect the pattern, then apply it in Find & Replace.
Why does my pattern match nothing?
Common causes are a missing g flag, unescaped special characters like . or (, or case sensitivity. Check the highlighted matches and group output to see what the engine is actually capturing.

↳ Curious to go deeper? Read the Regex cheatsheet with live tester guide →

// works with your data

Find & Replace Text Diff Case Converter Sort & Dedupe Lines Slug Generator

Use this via API

Get a free API key → 
curl -X POST https://thesnaptools.com/api/v1/tools/regex-tester \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"pattern":"pattern: \\w+@\\w+\\.\\w+ text: contact ada@example.com or dev@test.org"}'