Regex Tester & Debugger
A premium client-side regular expression tester. Enter your regex pattern and modifiers to instantly visualize matches in your test string, inspect capture groups, and validate expressions safely.
Regular Expression Pattern
Regex Analysis
Match Captures
Quick Regex Reference Cheatsheet
Character Classes
- . - Any character except newline
- \d - Any decimal digit [0-9]
- \D - Any non-digit
- \w - Word character [a-zA-Z0-9_]
- \s - Whitespace char
Quantifiers
- * - 0 or more occurrences
- + - 1 or more occurrences
- ? - 0 or 1 (optional)
- {n} - Exactly n times
- {n,m} - Between n and m times
Anchors & Groups
- ^ - Start of line / string
- $ - End of line / string
- \b - Word boundary anchor
- (...) - Capturing group
- (?:...) - Non-capturing group
Safe, Secure & Fast Client-Side Regex Parsing
Regular expressions are extremely powerful for scanning, editing, and validating text patterns (like searching for emails, phone numbers, zip codes, URLs, or parsing logs). However, pasting raw proprietary documents or configuration strings into third-party cloud-based regex platforms presents serious privacy vulnerabilities.
Our FlowStack **Regex Tester** computes all matches locally within your own browser engine using standard web capabilities. Your input data, documents, strings, and regex patterns are never submitted to any cloud API, keeping your credentials and proprietary source code completely secure.
Mastering Regular Expressions modifiers
Modifiers (or flags) significantly alter the behavior of a regular expression. By toggling global (g) search, your regex engine will extract every occurrence throughout the text instead of halting after the first match. Case-insensitivity (i) streamlines search profiles, so you do not need to explicitly declare upper-and-lower combinations.
Using the visual match highlighter above, you can test how capturing groups align, inspect exact character indexing, check matching speed in milliseconds, and debug complex expressions before deploying them in your JavaScript, Python, PHP, or Java application.
Frequently Asked Questions
How does the Regex Tester work?
The Regex Tester is a client-side JavaScript utility. When you enter a regex pattern, modifiers, and test string, it dynamically builds a RegExp object and executes it against the test string, highlighting matches and extracting capture groups in real-time.
Are my regex patterns or test data secure?
Yes, 100%. All processing is performed strictly inside your web browser. No data, regex patterns, or confidential text blocks are uploaded to any external server.
What regex engine does this tool use?
This tool uses the native JavaScript RegExp engine of your browser, which supports standard regular expression syntax including lookaheads, lookbehinds, unicode, and standard modifiers.
What do the modifier flags (g, i, m, s, u) mean?
Modifiers alter search behavior: "g" (global) finds all matches instead of stopping at the first; "i" ignores case; "m" enables multiline matching for ^ and $ anchors; "s" allows the dot (.) to match newline characters; "u" enables Unicode support.