Regex Tester Pro
Test regular expressions with real-time match highlighting. Matches are visually marked as you type — no submit button needed. Supports all flags, capture group inspection, JavaScript/Python/Ruby flavor notes, and 6 built-in presets for email, URL, IPv4, phone, and more.
All processing happens in your browser — nothing is sent to any server.
Real-World Use Cases
1. Validating Email Addresses in a Sign-Up Form
You need a regex to validate email input before hitting the backend. Test the pattern against valid and invalid addresses to make sure edge cases like [email protected] are handled.
Pattern
^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ Test Strings & Results
[email protected] → ✓ Match [email protected] → ✓ Match @missing-local.com → ✗ No match no-at-sign.com → ✗ No match
2. Extracting Timestamps from Server Logs
Parse Nginx or Apache log lines to extract the timestamp using named capture groups. This regex pulls out the date-time string from a standard combined log format line.
Pattern
\[(?<timestamp>\d{2}/\w{3}/\d{4}:\d{2}:\d{2}:\d{2}\s[+-]\d{4})\] Input & Captured Group
Input: 192.168.1.1 - - [05/Apr/2026:14:23:01 +0800] "GET /api" timestamp → 05/Apr/2026:14:23:01 +0800
3. Finding All TODO Comments in Code
Scan a codebase snippet for TODO, FIXME, or HACK comments and capture the message text after them. Use the gi flags for global, case-insensitive matching.
Pattern (flags: gi)
(TODO|FIXME|HACK):\s*(.+)$
Matches
// TODO: refactor auth middleware /* FIXME: race condition on concurrent writes */ // HACK: workaround for Safari bug
How to Use — Step by Step
- Enter your regex pattern — Type or paste your regular expression into the pattern field. The tool parses it in real-time and shows any syntax errors immediately.
- Set flags — Toggle flags like
g(global),i(case-insensitive),m(multiline) depending on your use case. Most pattern testing starts withgenabled. - Paste test text — Add the text you want to test against. Matches are highlighted in yellow as you type — no submit button needed.
- Inspect capture groups — Expand the Match Details panel to see each capture group (
g1,g2…) and named groups for every match. - Try presets — Use the 6 built-in presets (Email, URL, IPv4, Phone, Date, HTML Tag) as starting points, then customize for your exact requirements.
Frequently Asked Questions
How does real-time match highlighting work?▼
As you type your regex pattern, the tool instantly highlights all matching substrings in your test text. Yellow highlights show exactly where your pattern matches — no need to scroll through match lists manually.
What regex flavors are supported?▼
Testing always runs in your browser's JavaScript engine (ES2020+), which supports lookahead, lookbehind, named capture groups, and Unicode property escapes. Python and Ruby mode display flavor-specific syntax notes while running tests with the JS engine as a close approximation.
How do capture groups work?▼
Add parentheses around parts of your pattern to create capture groups: ([a-z]+). The Match Details section shows each captured group value (g1, g2…) alongside the full match. Named groups (?<name>…) are also supported.
What do the flags mean?▼
g (global): find all matches, not just the first. i (ignore case): A matches a. m (multiline): ^ and $ match line beginnings and ends. s (dot-all): . matches newlines. u (unicode): enable full Unicode support for \u{...} and \p{...}.
Is my data safe when using this tool?▼
Yes. Everything runs 100% in your browser. Your regex patterns and test strings are never sent to any server. All processing is local to your machine.
Why does my regex match too many or too few results?▼
Check your flags — without g (global), only the first match is found. Without m (multiline), ^ and $ match the full string boundaries, not line boundaries. The i flag makes matching case-insensitive. Try the presets to see working examples.
Need batch assertion testing?
Regex Tester (with pass/fail assertions) →Related Products
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