Regex Tester
Test and validate regular expression patterns against sample text strings in real-time. Features live match highlighting, capturing group inspection, flag customization (/g, /i, /m, /u), and instant presets for emails, URLs, IP addresses, and dates. All patterns and text strings are evaluated locally in your browser JavaScript engine, with no server transmission.
Quick Presets
Match Details
Client-Side Processing
Input regex patterns and sample test strings are never sent to an external server. All evaluation happens in your local browser sandbox, keeping confidential data and proprietary source code off any server.
Serverless Real-Time Regular Expression Tester & Debugger
Eliminate syntax errors and test complex capturing groups with sub-millisecond execution directly in your browser. Fully functional offline with multi-language code export.
Real-Time Match Highlighting & Group Breakdown
Highlights matched character spans instantly and enumerates parenthesized capturing groups with indexed positions.
One-Click Standard Validation Presets
Instantly load validated industry-standard regular expressions for emails, URLs, IPv4 addresses, UUIDs, and date strings.
Multi-Language Code Snippet Generation
Export your tested regex into ready-to-run code snippets for JavaScript/TypeScript, Python, Java, and C#.
Essential Regular Expression Syntax Cheatsheet
Quick reference for common escape sequences and metacharacters.
| Metacharacter | Description & Role | Matching Example |
|---|---|---|
| \d | Any digit (0-9) | \d+ -> matches "123" |
| \w | Alphanumeric word character (A-Z, a-z, 0-9, _) | \w+ -> matches "user_01" |
| \s | Whitespace character (space, tab, newline) | hello\sworld -> matches "hello world" |
| ^ / $ | Start of line (^) and end of line ($) | ^https -> matches string starting with "https" |
| * / + / ? | Quantifiers: 0+ (*), 1+ (+), 0 or 1 (?) | a+ -> matches "a", "aaa" |
| () / [] | Capturing group () and character set [] | [a-z]{3} -> matches "abc" |
Developer Implementation Snippets for Regex Matching
Standard integration code patterns across major programming ecosystems.
// Email pattern validation
const regex = /^([a-zA-Z0-9._-]+)@([a-zA-Z0-9._-]+\.[a-zA-Z0-9_-]+)$/;
const isMatched = regex.test("[email protected]"); // true
const match = "[email protected]".match(regex);import re
pattern = r"^([a-zA-Z0-9._-]+)@([a-zA-Z0-9._-]+\.[a-zA-Z0-9_-]+)$"
match = re.search(pattern, "[email protected]")
if match:
print(match.group(1)) # "user"import java.util.regex.*;
Pattern pattern = Pattern.compile("^([a-zA-Z0-9._-]+)@(...)");
Matcher matcher = pattern.matcher("[email protected]");
boolean isFound = matcher.find();using System.Text.RegularExpressions;
Regex regex = new Regex(@"^([a-zA-Z0-9._-]+)@(...)");
Match match = regex.Match("[email protected]");
if (match.Success) { string user = match.Groups[1].Value; }Essential Regex Presets for Form Validation
The most commonly required validation patterns in production web applications.
Email Address Validation
`^([a-zA-Z0-9._-]+)@([a-zA-Z0-9._-]+\.[a-zA-Z0-9_-]+)$` matches standard email format with usernames and domain extensions.
Phone Number Validation
`^\+?[0-9]{1,3}?[-.\s]?\(?[0-9]{1,4}?\)?[-.\s]?[0-9]{1,4}[-.\s]?[0-9]{1,9}$` handles international format with country codes.
IPv4 Address Validation
`^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$` checks valid 0.0.0.0 to 255.255.255.255 IP addresses.
Step-by-Step Regex Tester Guide
Step 1: Configure Pattern and Flags
Enter your regular expression in the top input and toggle /g, /i, /m, or /u flags as needed.
Step 2: Enter Test String
Type or paste sample text in the test string editor below to observe real-time matching highlights.
Step 3: Inspect Matches and Export Code
Review group matches in the side card and click "Export Code" to generate language-specific implementation snippets.
Frequently Asked Questions (FAQ)
Q.Are my regular expressions or test strings sent to any remote server?
No. All pattern evaluations run locally in your browser's JavaScript engine.
Q.What do the flags (/g, /i, /m, /u) do?
/g searches all occurrences globally rather than stopping at the first match. /i enables case-insensitive matching. /m treats ^ and $ as beginning/end of each line. /u enables full Unicode support.
Q.How does the tool alert me to regex syntax errors?
If a quantifier or bracket is malformed, an "Invalid Regular Expression" warning will appear with the underlying JavaScript syntax error message.
Q.What is a Capturing Group?
A parenthesized sub-expression () within a regex that extracts and isolates specific substrings from the overall match.
Q.Can I copy code snippets directly for my project?
Yes. Click the "Export Code" button on Toolbase Regex Tester to copy ready-to-use snippets in JavaScript, Python, Java, or C#.