Regex Tester Guide
Test regular expressions with real-time match highlighting, regex flags, capture groups, and common presets.
Overview
Test and debug regular expressions in real time with visual match highlighting, capture group extraction, flags support, and instant regex presets.
When to Use Regex Tester
Use Regex Tester when writing search, replacement, or validation logic for web applications, form validation, data extraction, or log parsing.
Inputs, Formats & Specifications
- Accepted Inputs
- Regex pattern, flag selectors (`g`, `i`, `m`, `s`, `u`), sample test string
- Output Formats
- Live highlighted match preview, match count, captured groups table, execution status
- Supported Standards
- ECMAScript (JavaScript) Regular Expressions
- Browser Limits & Scope
- Conforms to modern ECMAScript RegExp standards. Specialized PCRE-only constructs (such as recursive subpatterns `(?R)`) are not supported in standard JavaScript engines.
How to use Regex Tester
- Type or choose your regular expression pattern in the pattern input.
- Select active regex flags: `g` (global), `i` (case-insensitive), `m` (multiline), `s` (dot-all), `u` (unicode).
- Paste your test string into the text input area.
- View highlighted matches in real time along with match counts, match index ranges, and captured group values.
Real-World Examples
Frequently Asked Questions
What do the regex flags mean?
`g` searches for all occurrences rather than stopping after the first match; `i` makes matching case-insensitive; `m` treats `^` and `$` as matching the start/end of each line; `s` allows `.` to match newline characters.
Are common preset patterns available?
Yes. You can select one-click presets for common validations including emails, URLs, IPv4 addresses, phone numbers, and dates.
How does the tool prevent browser freeze from catastrophic backtracking?
The evaluation engine runs inside an execution time-slice guard that safely aborts if an exponential backtracking pattern stalls the main thread.
Privacy & Data Security
Regex Tester is designed to run in the browser. Review outputs before sharing them with any external service or workflow.