Regex Tester & Explainer
Free online regex tester with live highlighted matches, capture groups, replace preview, a plain-English explainer and JSON/CSV match export.
Enter a pattern above to see matches.
No matches found in the test string.
Enter a pattern to get a plain-English breakdown.
Flags:
Common patterns — tap to load
Why you’ll love Regex Tester & Explainer
Instant & free
No signup, no paywall, no limits — Regex Tester & Explainer works the moment the page loads.
Completely private
Everything runs in your browser. Nothing you enter is ever uploaded or stored on a server.
Works on any device
Fully responsive and touch-friendly — use it on your phone, tablet or desktop.
Built by developers
Accurate, fast and keyboard-friendly — the details developers care about.
How to use it
Open it
No download and no login — the tool is ready right at the top of this page.
Use it
Enter your details or start interacting. Everything updates live as you go.
Get your result
Copy, download or share your result in a single tap. That’s it.
About Regex Tester & Explainer
This regex tester runs your pattern against real text as you type, using the JavaScript (ECMAScript) engine — the same flavor that runs in every browser and in Node.js. Matches are highlighted directly inside the test string, and each one appears in a match list with its character index and every capture group, both numbered ($1, $2…) and named ((?<name>…)). All six JS flags — g, i, m, s, u and y — toggle with one tap.
It goes well beyond matching. A Replace panel previews String.replace() output with $1, $2 and $& substitutions. An export bar copies every match and its groups as JSON or CSV, ready for a spreadsheet or script. The Explain tab breaks the pattern into tokens and describes each one in plain English, and the Cheatsheet tab pairs a syntax reference with tap-to-load presets for emails, URLs, IPv4 addresses, hex colors, dates, phone numbers and more. A Share button packs the pattern, flags and sample text into a link you can send to a teammate.
Your text never leaves the browser, and a built-in safety net makes the tester hard to freeze: patterns with classic catastrophic-backtracking signatures (like nested quantifiers) are detected and tested against a reduced sample, very large inputs are capped, and matching runs under a one-second budget — so even a hostile regex can't lock up the page.
Popular uses
Frequently asked questions
JavaScript (ECMAScript), exactly as implemented by your browser — so results match what you'll get in Node.js, Deno and front-end code. Core syntax carries over to PCRE (PHP), Python and Java, but PCRE-only features such as \K, possessive quantifiers (a++) and recursion are not valid here. If the pattern will ship in another language, confirm it in that environment too, especially for lookbehind and Unicode handling.
Patterns like (a+)+, (.*)* or repeated overlapping alternations can force the engine to try an exponential number of paths — a few dozen characters of input can hang a browser tab. The tester spots these signatures and automatically limits the sample it tests so the page stays responsive. The fix is usually to make the inner part more specific (e.g. [^,]+ instead of .+) or remove one layer of repetition.
Wrap part of the pattern in parentheses, or use a named group like (?<year>\d{4}). Every match card then lists each group's value with its number and name, and the JSON/CSV export includes them as columns — handy for pulling structured data out of logs. In the Replace panel, reference groups with $1, $2 or $& for the whole match.
g (global) finds every match anywhere in the text; without it the engine stops after the first match. y (sticky) is stricter: it only matches starting exactly at the current position, which is mainly useful for writing tokenizers that consume input piece by piece. For everyday searching and extraction, g is the flag you want.
No. Matching, highlighting, explanation and export all run locally in your browser, and your work is saved only to this device's local storage. Even the Share button keeps data out of server logs: it encodes the pattern and text into the URL fragment (the part after #), which browsers never transmit to a web server.
Regex Tester & Explainer is 100% free — no signup, no watermarks and no usage limits. It’s one of 200+ free tools we build and give away.
Never. Everything is processed locally in your browser — safe for secrets, tokens and proprietary code.
More Developer Tools
From our collection of 317 free tools.
People also use
We built this. We can build yours.
Regex Tester & Explainer is one of 200+ free tools from Workaholic Developers — a software & AI studio. Need a website, app, AI agent or automation? Let’s talk.
🇮🇳 Built by Workaholic Developers
We built this little toy in days. Imagine what we’ll build for you.
AI agents, web apps, automation, custom tools — designed and engineered fast, on whatever tech fits the job. If you can describe it, we can build it.