Online Regular Expression Tester & Debugger
Test and debug regular expressions in real-time with visual match highlighting, capture group extraction, and polyglot code generation. 100% private in-browser tool.
At a glance
Regular Expression Tester & Debugger is a free, client-side tool that tests and debugs regular expressions in real-time with visual match highlighting, capture group extraction, replacement, and cheat sheets. Instant match calculations as you type with flag customization. All processing is local: nothing is uploaded, and no account is required.
100% In-Browser Pattern Evaluation
All regular expression matching, grouping, and replacement run locally in your browser memory via native JavaScript engine. Zero text is transmitted.
Use $1, $2 for captured groups, or $& for the entire matched string.
Match Inspector & Capture Groups Detailed offsets & numbered groups
| # | Range | Matched String | Capture Groups |
|---|
Implementation Code Snippets
Regular Expression Quick Reference
Character Classes
\d: Any digit (0-9)\D: Any non-digit\w: Word char (a-z, A-Z, 0-9, _)\s: Whitespace (space, tab, nl).: Any char (except newline)
Anchors
^: Start of string / line$: End of string / line\b: Word boundary\B: Non-word boundary
Quantifiers
*: 0 or more times+: 1 or more times?: 0 or 1 time (optional){3}: Exactly 3 times{2,5}: Between 2 and 5 times
Groups & Logic
(abc): Capture group(?:abc): Non-capturing groupa|b: Either a or b[a-z]: Any character in set[^a-z]: Negated set
How to Use This Regex Tester
Enter Regular Expression
Type your regex pattern and toggle desired flags (g, i, m, s, u), or click one of our common presets.
Provide Test Text
Paste or type the text you want to evaluate against. Matches are calculated in real-time as you type.
Inspect & Export
Examine matched tokens, inspect numbered capture groups, or copy implementation code in JavaScript, Python, or Go.
Frequently Asked Questions
What do the regex flags (g, i, m, s, u) mean?
The 'g' flag finds all matches rather than stopping at the first; 'i' makes matches case-insensitive; 'm' treats start and end characters (^ and $) as working across each line; 's' allows the dot (.) to match newlines; and 'u' enables full Unicode support.
Can I test regex substitution and replacement?
Yes. Switch to the Replacement view, enter your replacement string using $1, $2, or $& references, and preview the transformed output instantly.
Is my test text uploaded to any server?
No. All regular expression parsing and string evaluation run locally in your web browser via standard JavaScript V8 regex engine. Zero data is transmitted.
Why Use This Regular Expression Tester & Debugger?
How to Use Regular Expression Tester & Debugger
Enter Regular Expression
Type your regex pattern and toggle desired flags (g, i, m, s, u).
Provide Test Text
Paste or type the text you want to test against, or click a common preset.
Inspect Matches & Export
View highlighted matches, examine capture groups, or copy generated code in JavaScript, Python, or Go.
Email Extraction: Regex Pattern Matching Two Addresses
The engine builds a native RegExp object and iterates matches with String.matchAll, extracting capture groups and computing replacement previews entirely in browser memory.
Pattern: [a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,} Text: Contact support@example.com or admin@test.org
2 matches found: support@example.com (index 8), admin@test.org (index 30). Replacement with [EMAIL] applied.
Technical Specifications & Engine Details
| Specification | Details |
|---|---|
| Supported Formats | REGEX-PATTERN, TEXT → MATCHES, CAPTURE-GROUPS, REPLACED-TEXT, CODE-SNIPPETS |
| Execution Mode | 100% Client-Side In-Browser (client) |
| Browser Requirements | Requires modern web browser with ECMAScript 6+ and standard DOM Web APIs. |
| Performance Constraints | Client browser memory limit (typically 1–2 GB RAM); processing speed depends on local device CPU. |
100% Client-Side Privacy Guarantee
All regular expression evaluation runs locally in your browser memory. Zero patterns or text data are transmitted to external servers.
Frequently Asked Questions
What do the regex flags (g, i, m, s, u) mean?
Can I test regex substitution and replacement?
Is my test text uploaded to any server?
Methodology
This tool runs entirely in your browser. The example above shows a representative input and the result it produces.
Last updated .