Regex Tester & Debugger Online Free
Test, evaluate, and troubleshoot regular expressions (Regex) in real time directly in your browser. Features live visual match highlighting, flag toggles (`g`, `i`, `m`, `s`), numbered capture group inspection, and instant presets for emails, URLs, and dates.
Regex Tester & Debugger In-Browser Workspace
Input data or select files to begin. 100% private, client-side execution with zero server transmission.
How to Use Regex Tester & Debugger
- Step 1: Enter your regular expression pattern between the forward slashes (e.g. `[a-z0-9]+`).
- Step 2: Toggle desired matching flags: `g` (global), `i` (case-insensitive), `m` (multiline), or `s` (dot matches newlines).
- Step 3: Paste your sample text into the 'Test String' editor box.
- Step 4: Inspect the color-highlighted matches in the real-time preview panel.
- Step 5: Review the detailed inspection table below for matched indices, character positions, and capture groups.
About Regex Tester & Debugger
Regular expressions are powerful pattern-matching engines utilized across software engineering, log parsing, data sanitization, and input form validation. However, intricate regex syntax involving lookaheads, greedy quantifiers (`.*`), and capturing groups (`(...)`) is notoriously tricky to debug without live feedback. A faulty expression can lead to catastrophic backtracking or silent validation bypasses. Our Browser Regex Tester evaluates patterns using JavaScript's native RegExp V8 compilation engine. It runs non-blocking executions, captures index offsets, identifies distinct capture group extractions, and surfaces detailed syntax error messages. Because execution occurs entirely in your browser sandbox, you can safely test proprietary API keys, internal IP addresses, and private user credentials without cloud telemetry.
Frequently Asked Questions
What do the regex flags (g, i, m, s) mean?
`g` (global) finds all matches rather than stopping at the first; `i` ignores letter casing; `m` treats start `^` and end `$` anchors across individual lines; `s` allows the dot `.` metacharacter to match newline characters.
What regex flavor does this tool use?
The tool uses ECMAScript (JavaScript) regular expressions, the universal standard for modern web browsers, Node.js, and Chromium.
Can I inspect capture group values (, )?
Yes. When parentheses `()` are used in your expression, the results table breaks down each numbered capture group with its exact matched substring.
Are my test strings uploaded to a server?
No. All regular expression compilation and matching execute 100% locally in your device's browser memory.