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Test, Deconstruct &
Build Regular ExpressionsFlawlessly.

A precision-engineered developer suite for regex pattern engineering. Test matches with real-time capture group highlighting, parse cryptic legacy expressions into plain English token breakdowns, and assemble reliable patterns visually — entirely in your browser memory.

Open Regex Tester Compare Features

ECMA-262

Native JS Engine

Real-Time

Instant Evaluation

100%

In-Browser

Live Engine

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// Pattern: /([a-z0-9_\.\-]+)@([a-z0-9\-]+)\.([a-z]{2,5})/gm
const regex = /([a-z0-9_\.\-]+)@([a-z0-9\-]+)\.([a-z]{2,5})/gm;

// Real-time Matches:
✓ support@codekivo.com [$1: support, $2: codekivo, $3: com]
✓ dev.lead@acme-corp.org [$1: dev.lead, $2: acme-corp, $3: org]
✗ invalid_format#host.com (no match)

Valid ECMAScript Pattern

UTF-82 Matches0.4 ms

Specialized Regex Engineering Tools

Choose a dedicated utility designed specifically for live test matching, AST pattern deconstruction, or visual expression generation.

Core Engine

Regex Tester & Matcher

Test regular expressions against dynamic sample vectors in real-time. Highlights every match index, extracts numbered/named capture groups, and formats replacements.

ECMAScriptCapture GroupsSafety Bounds

Real-time match highlighting and capture group inspection
Full support for g, i, m, s, u, y, and d modifier flags
Cap on match count (2,500) and zero-length match loop safeguards

Launch Regex Tester

AST Inspector

Regex Explainer & Parser

Deconstruct complex and cryptic regular expressions into plain English steps. Demystifies lookaheads, lookbehinds, quantifiers, and complex character sets.

Grammar ASTLookaroundsPlain English

Deconstructs nested expressions into plain English steps
Explains lookarounds, quantifiers and capture groups
Highlights exact character classes and range semantics

Launch Explainer

Visual Composer

Regex Visual Builder

Assemble reliable regular expressions visually without memorizing arcane escape syntax. Combine presets, character classes, and quantifiers with point-and-click ease.

No-Code BlocksPreset LibraryInstant Preview

Visual point-and-click regex construction blocks
Presets for emails, URLs, dates, phones and IPs
Instant live test preview with copyable output

Launch Regex Builder

Seamless Regular Expression Pipeline

From visual pattern composition and preset selection to real-time match verification and AST audits.

Stage: Compose

Visual Pattern Building

Use the Regex Builder to assemble custom rules for emails, UUIDs, dates, or passwords without memorizing complex escape syntax.

Open Regex Builder

Stage: Verify

Real-Time Match Validation

Paste positive and negative test cases into the Regex Tester to verify captures, index boundaries, and flag modifiers in real-time.

Open Regex Tester

Stage: Audit

AST Explanation & Review

Feed cryptic expressions into the Regex Explainer to audit lookaround assertions, detect backtracking risks, and document patterns for pull requests.

Open Regex Explainer

Capability Matrix & Engine Support

Compare parsing engines, modifier flags, and debugging capabilities across our regex utility suite.

Specification	Regex Tester & Matcher	Regex Explainer	Regex Visual Builder
Core Objective & Target	Live Match Evaluation & Group Extraction	Deep AST Pattern Deconstruction	No-Code Visual Regex Composition
ECMAScript Engine & Standards	Native Browser Engine (ECMA-262)	Lexical Grammar AST Tokenizer	Strict ECMAScript Emitter
Flag Toggles (g, i, m, s, u, y)	Real-time Switch with Dynamic Re-run	Flag Impact Analysis & Scope Breakdown	Context-Aware Flag Pre-configuration
Capture Group Inspection	Visual Highlighting ($1, $2, Named Groups)	Decoupled Numbered & Named Group Hierarchy	Visual Group Enclosure & Quantifiers
Evaluation Safeguards & Warnings	2,500 Match Cap & Loop Safeguards	Structural Nesting & Repetition Warnings	Pre-vetted Non-Backtracking Templates
Data Privacy & Security	100% In-Browser (Zero Network Egress)	100% In-Browser (Zero Network Egress)	100% In-Browser (Zero Network Egress)
Execution Benchmark & Speed	Real-Time Reactive Match Evaluation	Instant Client-Side Tokenization	Instant Multi-Language Code Generation

Production-Tested Regex Presets

Battle-tested regular expression patterns commonly used in web applications, API input validation, and data extraction.

Email Address (RFC 5322)

RFC

Validates standard user mailboxes and domain extensions.

^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$

Test in Matcher Explain AST

URL / Web Address (HTTP/HTTPS)

RFC

Matches secure or standard web protocols with optional query paths.

^https?:\/\/[\w.-]+(?:\.[\w\.-]+)+[\w\-\._~:/?#[\]@!$&'()*+,;=.]+$

Test in Matcher Explain AST

Strict IPv4 Address

RFC

Matches four dot-separated decimal octets within 0–255 ranges.

^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$

Test in Matcher Explain AST

ISO 8601 Date (YYYY-MM-DD)

RFC

Validates year, month, and day format according to ISO standards.

^\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])$

Test in Matcher Explain AST

URL Slug / Kebab-Case

RFC

Clean URL paths composed of lowercase alphanumerics and hyphens.

^[a-z0-9]+(?:-[a-z0-9]+)*$

Test in Matcher Explain AST

Strong Password Policy

RFC

Requires minimum 8 characters, uppercase, lowercase, number & symbol.

^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$

Test in Matcher Explain AST

Related Developer Toolkits

Essential companion tool suites for string transformations, data payload validation, and web styling.

Text & TypographyPopular: Case Converter · Text Compare

Zero-Telemetry Regex Evaluation & Log Privacy Guarantee

Client-Side Verified

Every regular expression compile, AST tokenization, match evaluator, and pattern explainer executes directly in your browser using client-side JavaScript engines. Production server log samples containing PII, customer records, and proprietary regex validation patterns never leave your browser tab.

100% In-Browser

Zero Log Telemetry

Volatile Memory Only