What does the Regex Tester tool do?

The Regex Tester from PowerSEOTools.online lets you write JavaScript regular expressions and test them against sample text in real time. It shows matches, capturing groups, flags and errors, and highlights matches directly in your test string.

Which regex flavor does this tool use?

This tool uses the JavaScript regular expression engine built into your browser. It supports common flags like g, i, m, s and u, as well as features supported by modern JavaScript runtimes.

Can I see capture groups and match positions?

Yes. The tool shows each match with its start index, full matched text, capturing groups and named groups when available. It also highlights matches inside the test string preview.

Can I use this regex tester for SEO and web development tasks?

Absolutely. You can use the regex tester for parsing URLs, validating email addresses, finding patterns in HTML, cleaning logs, refactoring content, and many other SEO and development tasks.

Regex Tester & Debugger

Q: Is my text or regex uploaded to your server?

No. All regex testing happens directly in your browser using JavaScript. Your patterns and test strings are never uploaded, stored or logged on our servers.

Test and debug JavaScript regular expressions with real-time matching, highlighting, flags and group details. Perfect for SEO tasks, log cleanup, URL parsing, validation and complex text processing.

Pattern & Test String

Write your regular expression pattern and test it against sample text. Matches update in real time as you type.

Regular expression pattern (without slashes)

Example: ^https?:\/\/(?:www\.)?([^\/]+) to capture domains from URLs.

g Global (find all matches) i Ignore case m Multiline (^ and $ per line) s Dot matches newlines u Unicode mode

Active pattern: /pattern/g

Test string

Matches, Groups & Preview

See which parts of your text match, along with capturing groups and positions.

● Waiting for pattern…

Flags used: g

Matches: 0

First match index: –

Capturing groups in pattern: 0

Flag details:

Highlighted preview

Start typing a pattern and test string to see matches highlighted here…

Pattern Stats

Pattern length (chars) 0

Bytes (UTF-8) 0

Capturing groups 0

Test String Stats

Characters 0

Lines 0

Bytes (UTF-8) 0

Free Online Regex Tester & Debugger

The Regex Tester from PowerSEOTools.online is a fast, browser-based tool for building and debugging JavaScript regular expressions. As you type your pattern and test string, it highlights matches, shows capturing groups, and reports any syntax errors. This makes it easier to create reliable patterns for SEO tasks, automation scripts, APIs, log processing and content cleanup.

Common Use Cases for Regular Expressions

SEO & analytics: Filter URLs in reports, rewrite paths, validate tracking parameters, or group pages by pattern.
Content cleanup: Remove tracking query strings, fix formatting issues, or replace repeated patterns in text.
Form validation: Validate emails, phone numbers, postcodes, usernames and other user input.
Log & data parsing: Extract IP addresses, status codes, timestamps or IDs from server logs and CSVs.
Refactoring & search/replace: Use regex in your editor to safely update HTML, templates or codebases.

How to Use the Regex Tester

Enter your pattern in the Regular expression box (without surrounding slashes).
Choose flags like g, i, m, s and u depending on your use case.
Paste or type sample data into the Test string area.
Click Run Test, or simply type to see instant updates.
Check the summary card for match count, first match index, group count and any errors.
Use the highlighted preview and match list to fine-tune your pattern.

Understanding Regex Flags

g – Global: Find all matches, not just the first one.
i – Ignore case: Treat uppercase and lowercase letters as the same.
m – Multiline: Make ^ and $ match the start and end of each line instead of the whole string.
s – DotAll: Make . match newline characters as well.
u – Unicode: Enable full Unicode mode for advanced patterns.

Privacy-Friendly and Browser-Based

All regex testing happens directly in your browser using JavaScript. Your patterns and test strings are not sent to any server, which makes this tool safe for confidential logs, client URLs, draft content and internal data.

For even more control over your text and code, combine this Regex Tester with other PowerSEOTools.online utilities such as the JSON Formatter, HTML Encoder/Decoder, URL Encoder/Decoder and Base64 Encoder/Decoder.