regex-tester

Test a pattern against sample text with live highlighting. Options are labeled to match .NET's RegexOptions enum. Uses JavaScript's regex engine under the hood — see notes below for where that differs from .NET.

client-side only RegexOptions mapped

pattern.regex

Pattern

IgnoreCase

Multiline (^ and $ match line boundaries)

Singleline (. matches newline too)

Find all matches (not just the first)

Test string

highlighted matches

Enter a pattern and test string.

// RegexOptions mapping

IgnoreCase → JS i flag — behaves the same way.
Multiline → JS m flag — same meaning in both: ^/$ match at line breaks, not just string start/end.
Singleline → JS s flag (dotAll). Careful: .NET's "Singleline" and JavaScript's naming here point at the same behavior (. matches \n) despite the confusingly similar name to Multiline — they're independent flags in both engines.

// where .NET regex and JS regex actually diverge

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For the vast majority of patterns you'll write in a backend service — validation, parsing, log scraping — .NET's regex engine and JavaScript's behave identically, since both are backtracking engines with very similar syntax. The differences that matter show up in a few specific spots:

Balancing groups ((?<name1-name2>...)) — a .NET-only construct for matching nested/balanced structures. No JS equivalent; a pattern using this can't be tested here.
Named group syntax — both support (?<name>...), so this one's actually fine across both.
Right-to-left matching (RegexOptions.RightToLeft) has no JS equivalent.
Possessive quantifiers and atomic groups — supported in .NET 7+, not supported in JS.

If your pattern only uses standard character classes, quantifiers, anchors, and groups (which covers most real-world validation patterns), what you see here will match .NET's behavior exactly.