Regex Playground

Test regex live — railroad diagrams + plain English explained

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Regex Playground is a free, browser-based tool that lets you test regex live — railroad diagrams + plain english explained — with zero signup, zero installation. Your data never leaves your browser. Part of 116+ free developer and business tools at wowhow.cloud, built and maintained by a team with 14+ years of hands-on development experience.

TOOLRegex Playground

//g

Load:

Test String2 matches

Match Results

#	Match	Position
0	[email protected]	14
1	[email protected]	33

Railroad Diagram

Plain English

one or more of any character in [a-z], then "@", then one or more of any character in [a-z], then ".", then 2 or more of any character in [a-z] Flags: global (find all matches)

About Regex Playground

Regular expressions are one of the most powerful — and most misread — tools in a developer's toolkit. The ECMAScript regex engine used by JavaScript, Node.js, and most web frameworks supports a rich feature set including named capture groups, lookbehind assertions, and Unicode property escapes introduced in ES2018. A playground that renders railroad diagrams transforms an abstract pattern like /^(?=.*[A-Z])(?=.*\d).{8,}$/ into a legible flowchart, cutting debugging time dramatically.

How It Works

Pattern matching runs the browser's native RegExp engine, which means results are identical to what you would get in Node.js or a modern browser environment. The engine evaluates the pattern against your test string using the selected flags and highlights every match position in real time as you type.

Railroad diagrams are generated by parsing the regex AST (abstract syntax tree) and rendering each token — literals, character classes, quantifiers, groups, alternation — as a directed graph where left-to-right flow represents the matching direction. Each node type is color-coded: green for literals, blue for groups, orange for quantifiers.

The plain English explainer traverses the same AST and generates prose descriptions for each node. A pattern like \b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\b is explained as "a word boundary, followed by one or more uppercase letters, digits, dots, underscores, percent signs, plus signs, or hyphens..."

Who Is This For

A developer writing an email validation function tests their pattern against 15 edge-case strings to verify it rejects missing TLDs but accepts plus-sign subaddresses.

A data engineer crafts a regex to extract ISO 8601 timestamps from messy log lines, using the railroad diagram to verify the optional milliseconds group fires correctly.

A security engineer builds an input sanitization pattern and uses the explainer to document it in plain English for a code review comment.

A junior developer learning regex uses the railroad diagram to understand how alternation and grouping interact in an existing pattern they inherited.

How to Use

Type your regex pattern and select flags (g, i, m)

Enter test strings — matches highlight instantly in real-time

View the railroad diagram for a visual breakdown of your pattern

Read the plain English explanation to understand each part

Frequently Asked Questions

JavaScript regex (ECMAScript). This is the same flavor used in Node.js, browsers, and most web frameworks.

A visual flowchart showing how the regex engine processes your pattern step by step. It makes complex patterns much easier to understand.

Patterns are saved in your browser's local storage. You can also share via URL — the pattern is encoded in the URL parameters.

The playground supports g (global — find all matches), i (case-insensitive), m (multiline — ^ and $ match line boundaries), s (dotAll — . matches newlines), and u (Unicode mode). Flags can be combined freely.

Wrap the part of your pattern you want to extract in parentheses. The match panel shows each capture group numbered from left to right. Named groups (using ?<name> syntax) are also labeled by name.

Yes. The explainer breaks down lookaheads, lookbehinds, backreferences, character classes, quantifiers, and alternation. For very complex patterns it explains each segment in sequence rather than attempting a single sentence.