What is a regex tester for?

A regex tester helps developers verify in real time whether a regular expression matches a target string, view all matches and capture groups, and debug regex patterns without running code.

Which flags are supported?

Supports g (global), i (case-insensitive), m (multiline), and s (dotAll — . matches newlines). Multiple flags can be combined.

How do I use capture groups?

Wrap sub-patterns in parentheses () to create capture groups, e.g. (\d{4})-(\d{2})-(\d{2}) extracts date parts. The results panel shows capture group content for each match.

What if the regex produces no matches?

Check that you haven't forgotten the g (global) flag, that case matches (add i flag if needed), and that escape characters are correct (e.g. \d in JS regex strings needs \\d).

Is my input data safe?

Completely safe. All operations run locally in your browser and no data is uploaded.

Regex Tester

Test regular expressions in real time and view matches and capture groups.

Regular Expression

//g

Flags:

Test String

Match Highlights 2 matches

Match Details

#1support@example.comindex: 14

Group 1: support

Group 2: example.com

#2admin@devtools.ioindex: 37

Group 1: admin

Group 2: devtools.io

How to Use

Enter your pattern in the Regular Expression box (no leading/trailing / needed).
Toggle flags as needed: g = global, i = case-insensitive, m = multiline, s = dotAll.
Paste your test text in the Test String box — results update in real time.
Yellow highlights show all matches. The list below shows capture groups for each match.

About Regular Expression Tester

Regular expressions (regex) are sequences of characters that define a search pattern. They are essential for text validation, parsing, and transformation in most programming languages. Key concepts include character classes ([a-z]), quantifiers (* + ? {}), anchors (^ $), groups (()), and flags (g for global, i for case-insensitive, m for multiline). This tester highlights all matches in real time as you type, helping you build and debug complex patterns immediately. Common use cases include email validation, URL extraction, log parsing, and data cleaning.

Use Cases

Form Validation

Test email, phone, URL patterns before implementing them in your application's validation logic.

Log Parsing

Build regex patterns to extract timestamps, error codes, or IPs from server log files.

Find & Replace

Prototype complex search-and-replace patterns with capture groups before running them on production data.

Data Extraction

Write patterns to scrape structured data from semi-structured text (CSV fields, HTML attributes, etc.).

Examples

Input

Pattern: \d{4}-\d{2}-\d{2}
Text: Today is 2024-01-15

Output

Match: 2024-01-15

\d{4} matches exactly 4 digits. The hyphen is a literal character between digit groups.

Input

Pattern: (\w+)@(\w+\.\w+)
Text: user@example.com

Output

Group 1: user
Group 2: example.com

Parentheses create capture groups. Group 1 captures the username, Group 2 the domain.

Common Pitfalls & Edge Cases

⚠Greedy quantifiers (.* ) can match too much. Use lazy (.*?) or be more specific with character classes.
⚠Backtracking in nested quantifiers like (a+)+ can cause catastrophic performance (ReDoS attacks).
⚠JavaScript regex doesn't support lookbehind in all browsers. Check compatibility for (?<=...) patterns.
⚠Remember to escape special characters: . * + ? ^ $ { } [ ] | ( ) \ when matching literals.

🔒 Data Privacy

Regex evaluation runs entirely in your browser's JavaScript engine. No text or patterns are sent to any server.