Regex Tester

Test regular expressions online with live pattern matching. Free regex tester showing all matches with index positions, lengths, and captured groups.

Test regular expressions with live matching
Pattern
//
Test String

Run a check to see results

APIPOST /api/v1/text/regex
5(13 votes)
1
checks performed
Try also: Text Analyzer
Run Check

Key Features

100% Free

No registration required, unlimited checks

Instant Results

Real-time analysis with detailed output

REST API Access

Integrate into your workflow via API

Accurate Data

Live queries to authoritative sources

What is Regex Tester?

The regex tester provides a live environment for writing, testing, and debugging regular expressions against sample text. As you type your pattern, matches are highlighted in real-time in the test string, with each match displaying its index position, length, and captured groups. Regular expressions are powerful pattern matching syntax used across virtually every programming language — JavaScript, Python, Java, Go, PHP, Ruby, and more — for text validation (emails, URLs, phone numbers), data extraction (parsing logs, scraping web pages), search and replace operations, and input sanitization.

This free online regex tester is used by developers building and debugging regex patterns before deploying them in code, data engineers writing extraction patterns for log parsing and ETL pipelines, system administrators creating grep and sed patterns for text processing, and students learning regular expression syntax with immediate visual feedback.

How to Use

  1. 1Enter your regular expression pattern in the pattern field (e.g., \d+ for numbers, [a-z]+ for words)
  2. 2Toggle regex flags as needed: g (global — find all matches), i (case-insensitive), m (multiline)
  3. 3Paste or type the test string to match against in the text area below
  4. 4View highlighted matches updating in real time as you modify the pattern or text
  5. 5Review match details: each match shows its index position, length, full match text, and captured groups

Who Uses This

System Administrators

Monitor and troubleshoot infrastructure

Developers

Debug network issues and integrate via API

SEO Specialists

Verify domain configuration and performance

Security Analysts

Audit and assess network security

Frequently Asked Questions

How do I test a regular expression online?
Enter your regex pattern in the pattern field and paste your test text in the area below. Matches are highlighted instantly in real-time as you type — no need to click a button. Each match displays its position in the string, length, the matched text, and any captured groups. You can toggle flags (global, case-insensitive, multiline, dotAll, unicode) to modify matching behavior. This is much faster than testing regex in code because you see results immediately and can iterate on the pattern interactively.
What regex flags are supported and what do they do?
The tool supports standard JavaScript regex flags: g (global) finds all matches instead of stopping at the first one — essential for finding every occurrence. i (case-insensitive) makes the pattern match regardless of uppercase or lowercase. m (multiline) makes ^ and $ match the start/end of each line instead of the entire string. s (dotAll) makes the dot (.) match newline characters as well. u (unicode) enables full Unicode support including emoji and non-Latin scripts. Toggle flags using the buttons next to the pattern input.
What is a capture group in regex?
A capture group is a part of your regex pattern enclosed in parentheses that extracts a specific portion of the match. For example, the pattern (\d{4})-(\d{2})-(\d{2}) matching against '2025-03-15' produces three capture groups: group 1 = '2025' (year), group 2 = '03' (month), group 3 = '15' (day). Capture groups are essential for extracting structured data from text. Named groups like (?name) make code more readable. The tool displays all captured groups for every match.
What are the most common regex patterns?
Frequently used patterns include: digit sequences (matches numbers), word characters (matches letters), whitespace matching, start-of-line and end-of-line anchors, word boundary markers, and non-greedy quantifiers. Practical applications include patterns for validating email addresses, matching URLs, detecting IP addresses in the format 0-255 dot-separated, parsing dates in YYYY-MM-DD format, and extracting phone numbers. The best approach is to start simple and iteratively refine your pattern using this tester's real-time feedback.
Can I use patterns from this tool in my programming language?
This tool uses JavaScript regex syntax, which is compatible with most modern languages with minor differences. Patterns work directly in: JavaScript/TypeScript, Java (similar syntax with minor differences in flags), Python (use re module — most patterns transfer directly), PHP (use preg functions — PCRE syntax is very similar), Ruby, Go, Rust, and C#/.NET. The main differences are in flag syntax and some advanced features like lookbehinds. Once your pattern works in this tester, adapting it to your target language usually requires only minor adjustments.

Related Articles

Ping tester — check your ping onlineGuide

Ping tester — check your ping online

Test your ping to any server instantly. Check latency in ms, understand jitter and packet loss, and find out how to reduce high ping.

NetVizor Team
Apr 4, 2026

Related Tools

Text Analyzer

Text Diff

JSON Formatter & Validator

Filler Word Checker

Popular Tools

DNS Lookup

WHOIS Lookup

Domain Age

Nameserver Checker

API Endpoint

POST /api/v1/text/regex
View Documentation