How does the tool prevent catastrophic backtracking (ReDoS)?

Execution is wrapped in safety boundaries with nested quantifier scanners, timeout limits, and execution error catching to prevent browser tab freezes.

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Regex Tester & Debugger

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Test and debug regular expressions.

100% In-Browser Execution

Regular ExpressionECMAScript (JavaScript Flavor)

Presets:

//g

Test String

90 chars

Interactive Match Highlighting

3 matches 0.16ms

Token-by-token automated AST breakdown:

/gGlobal (g)

Don't return after first match; find all occurrences across the string

(...)Capturing Group #1

Groups subpattern and saves the match into backreference Group #1 ($1).

@Literal '@'

Matches character '@' literally (case-sensitive)

(...)Capturing Group #2

Groups subpattern and saves the match into backreference Group #2 ($2).

Tool Documentation, Shortcuts & FAQs

How to Use Regex Tester & Debugger

1Enter your regular expression in the Pattern field (without enclosing slashes).
2Toggle your desired flags: g (global), i (case insensitive), m (multiline), s (dotAll).
3Type or paste your test text in the Test String area.
4Inspect the highlighted matches and check the token explanation and capture group table.

Key Capabilities

Live Match Highlighting

Visualizes all regex matches in your test string with alternating colors for adjacent matches.

Token-by-Token Explanation

Automated AST breakdown explaining anchors, quantifiers, character classes, and capture groups in plain English.

Capture Group Breakdown

Inspects full matches, numbered groups (Group 1, 2, etc.), and named capture groups.

Preset Regex Library

One-click templates for Email addresses, URLs, IPv4/IPv6, Phone numbers, Hex colors, and Slugs.

Interactive Flag Toggles

Easily toggle Global (g), Case-Insensitive (i), Multiline (m), DotAll (s), and Unicode (u) flags.

Frequently Asked Questions

It uses the native JavaScript RegExp engine of your browser (ECMAScript specification), ensuring 100% fidelity with your front-end and Node.js code.

Zero Data Retention

All calculations are performed strictly in client-side memory using your browser engine. No data is ever sent across the network.

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