What is Regex Tester?
Regular Expressions (Regex) are notoriously difficult to debug. Sending your test strings (which often contain real PII or production data) to cloud testers is a security risk. Our Regex Tester runs the matching engine locally in your browser, providing instant syntax highlighting and match groups without network latency.
Before you use this tool
Start with a small, representative example and check the result before you rely on it in a larger workflow. Keep the original data and look closely at the edge cases. The safest tool is the one whose limits you understand.
Deep Dive: Regex Tester
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“When I first learned regex, I thought it was just random symbols. But then I realized it's actually like a secret code for finding text. I built this tester to help me (and you!) see exactly what's matching in real-time.”
Azeem Mustafa
Privacy Architect
Core Capabilities
- Real-time live matching and visual highlighting
- Interactive Capture Group and Backreference breakdown
- Integrated Replace Tester with placeholder support
- Flags support: Global, Case-Insensitive, Multiline, DotAll, and Unicode
- Built-in Regex Cheat Sheet for quick syntax reference
- Match count and index tracking for precise debugging
- locally processed and private and runs entirely in your browser using local resources
Why It Matters
- Clarity: Visualize complex patterns before they reach your codebase.
- Speed: Build and test regex 10x faster than terminal trial-and-error.
- Learning: Understand how groups and flags work through direct visual feedback.
- Security: Test against private customer data or logs with zero leakage risk.
- Zero Overhead: No software to install, just a professional playground in your browser.
Quick Start Guide
Write Your Pattern: Enter your regex string. Notice how the tool automatically detects your syntax and starts looking for matches.
Select Your Flags: Toggle Global (g), Case-Insensitive (i), and Multiline (m) flags to match the behavior of your target environment.
Paste Test Data: Drop the text you want to search through into the main editor. Even if it is thousands of lines long, we handle it instantly.
Inspect the Highlights: See your matches update in real-time. We use distinct colors to help you distinguish between different capture groups.
Review Group Details: Check the sidebar to see the exact content and index of every captured group in your match result.
Test Replacements: Switch to the "Replace" mode to see how your text will look after transformations, including support for capture group placeholders.
Usage Examples
Email Validation (Simple)
Scenario 01Match basic email patterns
Pattern: \w+@\w+\.\w+ Test: [email protected]
Match! ✅ Matches "[email protected]"
Extract Phone Numbers
Scenario 02Find US phone numbers in text
Pattern: \d{3}-\d{3}-\d{4}
Test: Call me at 555-123-4567Match! ✅ Captures "555-123-4567"
Find and Replace
Scenario 03Swap first and last name
Pattern: (\w+) (\w+) Replace: $2, $1 Test: John Doe
"Doe, John" - capture groups swapped!
Common Scenarios
Email Validation in Forms
Test your email regex pattern before deploying.
Extract Data from Logs
Pull specific info from log files
URL Parsing
Extract domain from URLs in text.
Data Sanitization
Remove unwanted characters from input.
Questions?
Technical Architecture
Regex Basics - The Essential Tokens
**Characters**: - `.` = Any character (except newline) - `\d` = Any digit (0-9) - `\w` = Word character (a-z, A-Z, 0-9, _) - `\s` = Whitespace (space, tab, newline) **Negations** (uppercase = opposite): - `\D` = Not a digit - `\W` = Not a word character - `\S` = Not whitespace **Quantifiers**: - `*` = 0 or more - `+` = 1 or more - `?` = 0 or 1 (optional) - `{3}` = Exactly 3 - `{2,5}` = Between 2 and 5 - `{3,}` = 3 or more **Anchors**: - `^` = Start of string/line - `$` = End of string/line - `\b` = Word boundary Example: `^\d{3}$` = Exactly 3 digits, nothing else
Capture Groups Explained
**Basic Capture**: Use () to capture parts of match Example: `(\w+)@(\w+)` Matches: john@example - Full match: john@example - Group $1: john - Group $2: example **Use in Replace**: Pattern: `(\w+) (\w+)` Replace: `$2, $1` Input: 'John Doe' Output: 'Doe, John' **Non-Capturing Group**: `(?:...)` Groups for logic but doesn't capture: `(?:Mr|Mrs|Ms)\.? (\w+)` Matches title + name but only captures name **Named Groups**: `(?<name>...)` Example: `(?<user>\w+)@(?<domain>\w+)` Access by name instead of number! Capture groups are POWERFUL for extraction and transformation.
Flags (Modifiers) Explained
**g - Global**: Find ALL matches, not just first - Without: 'aaa'.match(/a/) = ['a'] (first only) - With g: 'aaa'.match(/a/g) = ['a','a','a'] (all) **i - Case Insensitive**: Ignore CAPS - Pattern: `/hello/i` matches Hello, HELLO, hElLo **m - Multiline**: ^ and $ match line boundaries - Without m: ^ = start of string only - With m: ^ = start of each line **s - DotAll** (newer):. matches newlines - Normally. doesn't match \n - With s:.* can match across lines **u - Unicode**: Full Unicode support - Enables matching emoji and special chars properly **y - Sticky**: Advanced, rarely used - Matches must start at lastIndex position Most common: Use /g for find all, /i for case-insensitive, /m for multiline text!
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Founder & Lead Developer at FileMint
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