Pattern Testing

RegexLens provides real-time regex testing with instant visual feedback. As you type your pattern, matches are highlighted immediately in your test text.

Live Match Highlighting

Every match is highlighted in your test text with distinct colors:

Full matches are highlighted with the primary color
Capture groups each get their own color for easy identification
Named groups display their names alongside the match

Example: Phone Number Matching

Pattern:

\((\d{3})\)\s*(\d{3})-(\d{4})

Test text:

Call us at (555) 123-4567 or (800) 555-1234

RegexLens will highlight both phone numbers and show you:

Group 1: 555 and 800 (area codes)
Group 2: 123 and 555 (exchange)
Group 3: 4567 and 1234 (subscriber)

Try this pattern → (opens in a new tab)

Regex Flags

Toggle any combination of JavaScript regex flags:

Flag	Name	Description
`g`	Global	Find all matches, not just the first
`i`	Case Insensitive	Match regardless of case
`m`	Multiline	`^` and `$` match line boundaries
`s`	DotAll	`.` matches newlines
`u`	Unicode	Enable full Unicode support
`y`	Sticky	Match only at `lastIndex` position

Flag Combinations

Common flag combinations for different use cases:

gi  - Find all matches, case-insensitive (most common)
gm  - Find all matches across multiple lines
gis - Find all matches including newlines in .

Match List

Below the test text, RegexLens displays a detailed match list showing:

Match index (0, 1, 2, ...)
Full match text
Start and end positions in the test text
Capture groups with their values
Named groups with their names and values

Truncation Protection

To keep the UI responsive, RegexLens limits:

Maximum 1,000 matches displayed
Maximum 50,000 characters in test text
Maximum 2,000 characters in pattern

If your pattern produces more matches, you'll see a "(truncated)" indicator.

Token Toolbar

Quickly insert common regex tokens with the toolbar below the pattern input:

Token	Meaning
`\d`	Any digit (0-9)
`\w`	Word character (a-z, A-Z, 0-9, _)
`\s`	Whitespace (space, tab, newline)
`.`	Any character (except newline)
`+`	One or more
`*`	Zero or more
`?`	Zero or one (optional)
`{}`	Exact quantifier
`()`	Capture group
`(?:)`	Non-capturing group
`[]`	Character class
`^`	Start anchor
`$`	End anchor
`\|`	Alternation (OR)
`\b`	Word boundary

Click any token to append it to your current pattern.

Keyboard Shortcuts

Speed up your workflow with keyboard shortcuts:

Shortcut	Action
`/`	Focus the regex editor
`Cmd/Ctrl + Enter`	Force re-parse
`Escape`	Clear selection
`Cmd/Ctrl + Shift + C`	Copy share link

Error Handling

When your pattern has a syntax error, RegexLens shows:

Red underline on the problematic part of the pattern
Error message explaining what's wrong
Error position so you know exactly where to fix

Common errors detected:

Unmatched parentheses ( or )
Invalid escape sequences \q
Invalid quantifiers {3,1} (min > max)
Unterminated character classes [abc

Getting Started Explanations