Which regex flavor is this?

JavaScript (the same engine as your browser). Most syntax transfers to Python, Java and PCRE, but lookbehind and some advanced features differ between flavors - always re-test in your target language.

Why is my pattern marked invalid?

The error message shows the browser's exact complaint - usually an unclosed bracket, a stray backslash, or a bad quantifier. Fix it in the pattern box and highlighting resumes instantly.

What's the difference between the g and m flags?

g (global) finds all matches instead of stopping at the first. m (multiline) makes ^ and $ match at line boundaries, not just the string's start/end. They're independent - you often want both.

How do capture groups work here?

Parentheses create numbered groups. Each match row expands to show group 1, 2, 3… with their captured text - use (?:…) for non-capturing groups when you don't need the value.

Is catastrophic backtracking a risk?

In this tester, a runaway pattern just freezes your tab briefly - close it if needed. In production code, avoid nested quantifiers like (a+)+ and prefer atomic groups or possessive quantifiers where your flavor supports them.

Developer Tools

Regex टेस्टर

Regex मैच नहीं हो रहा और समझ नहीं आ रहा क्यों? अपना पैटर्न और टेस्ट स्ट्रिंग पेस्ट करें — डिबग करते समय मैच लाइव चमकते हैं।

Pattern (without the / slashes /)

Flags

Test string

Common patterns

Regex cheatsheet

Character classes

.: Any character except newline
\d / \D: Digit / non-digit
\w / \W: Word char (A-Za-z0-9_) / non-word
\s / \S: Whitespace / non-whitespace
[abc]: Any of a, b, c
[^abc]: Anything except a, b, c
[a-z]: Range a through z

Quantifiers

*: 0 or more (greedy)
+: 1 or more (greedy)
?: 0 or 1
{n}: Exactly n
{n,}: n or more
{n,m}: Between n and m
*? +? ??: Lazy versions: match as little as possible

Anchors

^: Start of string (or line with m flag)
$: End of string (or line with m flag)
\b: Word boundary
\B: Not a word boundary

Groups

(abc): Capture group: numbered 1, 2, 3…
(?:abc): Non-capturing group
(?<name>abc): Named capture group
a|b: Alternation: a or b
\1: Backreference to group 1
(?=abc): Positive lookahead
(?!abc): Negative lookahead

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उपयोग कैसे करें Regex टेस्टर

अपना पैटर्न डालें. स्लैश के बिना regex टाइप करें, फिर ज़रूरत के हिसाब से फ़्लैग (g, i, m, s, u) टॉगल करें।
टेस्ट टेक्स्ट जोड़ें. जिस स्ट्रिंग से मैच करना है, उसे पेस्ट करें — लॉग, फ़ॉर्म इनपुट, जो भी हो।
मैच जांचें. मैच टेक्स्ट में हाइलाइट होते हैं; नीचे पैनल हर मैच को उसके कैप्चर ग्रुप समेत सूचीबद्ध करता है।
प्रीसेट आज़माएं. अटके? आम पैटर्न (email, URL, date…) लोड करें और अनुकूलित करें।