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Online Regex Tester, Visualizer & Railroad Diagram Studio

Deconstruct regular expressions into interactive visual state diagrams, inspect capture groups, test live matches, detect ReDoS risks, and generate code in 6 languages.

Quick Answer & Summary

A Regex Visualizer translates complex regular expressions into an interactive Abstract Syntax Tree (AST) and railroad diagram. Developers can inspect character classes, quantifier loops, and capture group boundaries in real-time, test matches against sample strings, and generate production code for Python, Go, Rust, Java, and JavaScript.

Non-Deterministic Finite Automaton (NFA) Model
M = (Q, Sigma, delta, q_0, F)

Every regular expression compiles to a finite state automaton where Q is the set of state nodes, Sigma is the alphabet, delta is the transition function, q_0 is the start anchor, and F is the accepting state.

Interactive Regex Studio & Visual AST Matcher

Deconstruct regular expressions into visual state graphs, test matches, and generate code.

Regular Expression Pattern
ReDoS: Medium
Valid Regex
//
Flags:
Test String / Corpus
0.83ms•
3 matches
●
Start
^
Start of String/Line
[a-zA-Z0-9._%+-]+
Character Set [a-zA-Z0-9._%+-]
@
Literal "@"
[a-zA-Z0-9.-]+
Character Set [a-zA-Z0-9.-]
\.
Escaped "."
[a-zA-Z]{2,}
Character Set [a-zA-Z]
$
End of String/Line
◉
End
Click on any token in the diagram above to inspect its semantics and quantifier rules.

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Toolbox Editorial TeamVerified Authors

Systems & Security Engineers • Applied Cryptography & High-Performance Web Tools

Updated:
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Standards AuditedRFC & ISO compliant
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Documentation & Guide

How to Use Online Regex Tester, Visualizer & Railroad Diagram Studio

1

Choose a Preset or Enter Custom RegEx

Select from 8 production presets (RFC Email, SemVer, ISO 8601 Date, JWT, IPv4, Markdown Links) or type your custom pattern in the pattern input bar.

2

Explore the Visual AST & Railroad Flow

Observe the graphical node sequence showing anchors (^, $), character sets, quantifier loops (⟲), and capture group boundaries.

3

Inspect Matches & Group Backreferences

Check match offsets, test string highlighted spans, and verify extracted named and numbered capture groups in the Match Inspector.

4

Generate Multi-Language Code Snippets

Switch to the Code Generator tab for instant, production-tested boilerplate in JavaScript, Python, Go, Rust, PHP, and Java.

Practical Examples & Conversions

Input
v2.14.3-alpha.1
Output
Captures: $<major>=2, $<minor>=14, $<patch>=3, $<prerelease>=alpha.1

Frequently Asked Questions (PAA)

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Authoritative Standards & Citations

Calculations and algorithms on this page are implemented and verified in strict accordance with the following official technical specifications:

IETF (Internet Engineering Task Force)

RFC 7519: JSON Web Token (JWT)

Standardized compact, URL-safe means of representing claims to be transferred between two parties.

W3C Recommendation

Web Cryptography API Specification

Standard JavaScript API for performing basic cryptographic operations in web applications.

IETF Standards Track

RFC 4122: A Universally Unique IDentifier (UUID) URN Namespace

Definition of uniform format and generation algorithms for UUIDs.