Regex Tester

Test regular expressions with live match highlighting, match count, and flag toggles.

//g
Test String

What is a Regex Tester?

A Regex Tester provides a real-time environment to write, test, and debug regular expressions against input text. Instead of guessing how a pattern behaves — or running a script every time — this tool gives immediate visual feedback with highlighted matches, match counts, and captured group details.

—Debugging patterns: Understand why a regex matches or fails to match.
—Input validation: Test email, URL, phone, and other format validators.
—Text extraction: Find and isolate patterns from logs or user input.
—Search & replace: Build advanced find/replace logic before integrating it.

Regex Flags Reference

gGlobal

Find all matches rather than stopping after the first.

iCase-insensitive

Match uppercase and lowercase letters interchangeably.

mMultiline

Make ^ and $ match the start/end of each line, not just the string.

Key Features

✓Live match highlighting — Matched text is highlighted inline as you type the pattern
✓Real-time execution — Results update on every keystroke — no submit button
✓Match count display — See the total number of matches at a glance
✓Flag toggles — Enable/disable g, i, and m flags with one click
✓Match details panel — View each match with its index position and captured groups
✓Error handling — Invalid patterns show a descriptive error immediately

Example

Pattern

\b\w+@\w+.\w+\b

Test String

Contact us at support@example.com or admin@test.org

Matches

1.support@example.com
2.admin@test.org
\bword boundary
\w+one or more word characters
@literal @ symbol
\.escaped dot

Common Use Cases

Input Validation

Validate email addresses, phone numbers, postal codes, credit cards, and other structured formats before processing.

Text Parsing

Extract specific data — IPs, dates, tokens — from log files, API responses, or user-generated content.

Data Cleaning

Remove or replace unwanted patterns such as extra whitespace, HTML tags, or non-printable characters.

Debugging Patterns

Test regex behavior with real input before embedding patterns into application code.

Search & Replace

Build and validate complex find/replace logic for editors or text processing pipelines.

Security Filters

Test input sanitization patterns to ensure malicious strings are correctly rejected.

Benefits for Developers

  • →Faster debugging: Real-time feedback eliminates the write-run-check cycle for regex testing.
  • →Visual understanding: Highlighted matches make it clear exactly what a pattern captures.
  • →Captures group detail: See each capture group value and its position in the match details panel.
  • →Reduces trial and error: Immediate error messages for invalid patterns prevent confusion.
  • →No backend required: Runs entirely in the browser using the native JavaScript RegExp engine.
  • →Secure: Your test strings — which may contain sensitive data — never leave your machine.

Frequently Asked Questions

What is regex?

Regex (regular expression) is a sequence of characters that defines a search pattern. It is used for matching, searching, and manipulating text in almost every programming language.

What are regex flags?

Flags modify how the regex engine interprets the pattern. g (global) finds all matches, i (case-insensitive) ignores letter casing, and m (multiline) changes the behaviour of ^ and $.

Can I test complex regex patterns?

Yes. The tool supports the full JavaScript RegExp syntax including lookaheads, lookbehinds, named capture groups, and Unicode character classes.

Is this tool safe to use?

Yes. All processing happens in your browser using the native JavaScript engine. No data is sent to any server.

Is this tool free?

Yes. The Regex Tester on NexoraTools is completely free with no sign-up or restrictions.