Developer tool

Regex Tester

Type a JavaScript-style pattern, paste sample text, and see matches highlighted in real time. Plain-English notes break down what each piece does—no server round-trip, everything runs in your tab.

Pattern

Flags

g — Global — find every match, not just the first.i — Ignore case — letters match in either case.m — Multiline — ^ and $ match line boundaries, not only the string ends.s — DotAll — . matches newline characters too.u — Unicode — treat pattern as Unicode code points; enables \p{…} when supported.y — Sticky — search only from the engine’s lastIndex (advanced).d — Indices — expose start/end positions for each capture (ES2022).

Quick samples

Test string

3 matches · 3 start positions

Say hello to Hello-world and hello again.

Highlighted spans update as you type. Scroll stays aligned between the highlight layer and the editor.

Plain-English walkthrough

Match a word boundary (between word and non-word).
Match the literal text “hello”.
Match a word boundary (between word and non-word).

g: Global — find every match, not just the first.
i: Ignore case — letters match in either case.

Match details

#	Index	Match	Captures
1	4	hello	—
2	13	Hello	—
3	29	hello	—

Replacement preview (JavaScript semantics)

Say <hello> to <Hello>-world and <hello> again.

Uses String.prototype.replace. For global replace-all semantics, include the g flag (this preview forces g when building the preview RegExp).

Complex regex engines differ slightly—this tool follows JavaScript’s RegExp in your browser. Very large inputs or catastrophic backtracking can freeze the tab; trim samples when debugging heavy patterns.

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Regex Tester — Live Matches & Plain-English Explanations

Test JavaScript regular expressions with live highlighting, match details, replacement preview, and plain-English pattern explanations—all running locally in your browser on Onlikit.

Regex Tester — Live Matches & Plain-English Explanations

Paste a pattern and sample string to see every match highlighted. The walkthrough translates anchors, character classes, groups, quantifiers, and lookarounds into plain language so you can confirm the regex does what you think before it reaches production.

Need to inspect JSON cut from logs first? Open the JSON Formatter. For JWT validation workflows, use the JWT Toolkit. Browse all utilities on Onlikit tools.

Built for day-to-day development

Live highlight layer — edits stay aligned with the colored match spans as you scroll
Flags at a glance — toggle `g`, `i`, `m`, `s`, `u`, `y`, and `d` with short reminders of what each does
Captures table — indices, full match text, and numbered groups for each result
Named groups — when your pattern uses `(?<name>…)`, values appear per match
Replacement preview — try `$&`, `$1`, or `$$` using the same rules as `String.prototype.replace`
Quick samples — load common patterns (email-like, dates, URLs) as a starting point

How processing works

The tester uses your browser’s native `RegExp` engine; nothing is uploaded to Onlikit servers. Performance still follows JavaScript rules: extremely large inputs or pathological patterns can stress the tab—trim text when testing heavy expressions.

When to double-check results

`RegExp` behavior can differ from PCRE, Python, or other engines. If you are shipping server-side validation, re-run the same pattern in that environment before you rely on it.