Regex Tester Pro - Test, Save & Explain Patterns

Test regex with live highlights, capture groups, replace, saved patterns, and step-by-step explanations. Offline.

Stop guessing at regex. Test, debug, and understand patterns the moment you type them, with live highlighted matches, named capture groups, replace preview, and a step-by-step plain-English explanation of every token. 🚀 🚀 Why developers love Regex Tester Pro Regex is everywhere - log filters, form validation, data scraping, code search, find-and-replace at scale - and every regex is one stray bracket away from matching nothing or everything. Regex Tester Pro turns trial-and-error into a tight feedback loop: paste your test text, type a pattern, and watch matches light up character-by-character. Hit a token you don't recognize? The Pro explanation tab walks you through the AST in plain English. Worried about catastrophic backtracking before pushing a validator to production? The performance profiler runs your pattern in a sandboxed Web Worker with timeouts so you catch the runaway before your users do. This is the regex tool that takes you from 'why is this matching nothing?' to 'oh, that's why' in seconds. ⚡ Everything in the free plan ✓ Live match highlighting as you type - JS regex engine ✓ Capture group display, both numbered and named ✓ Match count, position, and length per match ✓ All standard flags: g (global), i (case-insensitive), m (multiline), s (dotall), u (unicode), y (sticky) ✓ Replace mode with live preview ✓ Save up to 3 patterns to a personal library ✓ History of the last 5 tests, restored on next open ✓ Bundled cheatsheet of the 30 most-used tokens ✓ 5 starter patterns from the common-pattern library (email, URL, phone, IP, UUID) ✓ 100 tests per day - generous, no signup, no email 🔓 What Pro unlocks ✦ Step-by-step pattern explanation - the AST walker breaks any pattern into a readable tree: 'anchor: start of line', 'character class: lowercase a-z', 'quantifier: 1 or more, greedy', 'capture group #1: domain'. Hover any token, see the explanation. Built in - no API calls, no internet needed. ✦ 50+ pre-built patterns library - email RFC5322, URL, IPv4, IPv6, UUID v1-v5, ISO 8601 dates, semver, credit card (Luhn-aware), US phone, EU phone, US ZIP, slug, hex color, JWT, MAC address, base64, hex, GUID, Markdown link, and more. Click any pattern to load it into the tester instantly. ✦ Unlimited saved patterns - keep your team's regex library at hand. Tags, notes, and search across saves. ✦ Catastrophic backtracking detection - the performance profiler runs your pattern in a sandboxed Web Worker with a 1-second timeout, then reports backtracking score, runtime, and which subpattern is the suspect. Catch ReDoS bugs before they ship. ✦ Full history - last 100 tests instead of 5, with one-click restore. ✦ Searchable cheatsheet - 200+ tokens including PCRE-only, Unicode property escapes, lookbehind families, and atomic groups. Search by name or paste a token to learn what it does. ✦ Export test cases - save your pattern + test inputs + expected matches as a Jest, Vitest, or Mocha test file. One click. Drop it into your repo and your regex is protected by tests forever. ✦ Unlimited daily tests - for the engineers who debug 50 patterns a day. 🎯 Who it is for Backend engineers writing input validators. Frontend engineers wiring up form regex. Data engineers parsing CSV log lines. SREs writing alerting filters. QA engineers stress-testing input forms. Security researchers writing CTF and bounty payloads. Technical writers double-checking documentation samples. Anyone who has ever stared at /^(?:[a-z0-9!#$%&'*+\/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+\/=?^_`{|}~-]+)*)@(?:[a-z0-9]+(?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9]+(?:[a-z0-9-]*[a-z0-9])?$/i and wondered what it actually does. 🛠️ How it works 1️⃣ Pin the extension to your toolbar (one-time). 2️⃣ Click the icon to open the popup. 3️⃣ Type or paste a regex into the pattern field. Toggle flags from the row of buttons. 4️⃣ Paste your test text into the text area below. 5️⃣ Watch matches highlight live. Capture groups appear in a table. Match count and positions update on every keystroke. 6️⃣ Switch to Replace mode to see live replacement preview, or Explain (Pro) for the step-by-step breakdown. 💡 Real use cases → Validate that an email regex actually matches RFC-correct addresses without rejecting valid ones → Build a log line parser - capture timestamp, level, message - and verify on real logs → Find every TODO comment in a codebase paste with a single regex → Strip ANSI escape codes from terminal output → Test a password validator before shipping it to a signup form → Convert phone numbers to E.164 format with capture-group replace → Find every URL in a markdown file and check none are broken → Quick-fix a misbehaving find-and-replace inside an IDE by testing the regex outside it first 🔒 Privacy you can verify Your patterns and test text never leave the browser. Free regex evaluation runs locally in JavaScript. Pro AST explanation runs locally too - no API calls. The only network traffic the extension makes is a license check (sending a random device ID, no content) and anonymous funnel counts. No tracking pixels. No third-party analytics. No telemetry of patterns or text content. Open the network tab and verify yourself. 📊 Performance & benchmarks The regex engine runs against 1MB test strings in under 80ms on a typical laptop. The AST explanation walker handles patterns up to 10,000 characters in under 30ms. The whole bundle is ~95KB gzipped. Catastrophic backtracking detection runs in an isolated Web Worker with a hard 1-second wall-clock cap, so even a runaway like /(a+)+$/ on 'aaaaaaaaaa!' returns a 'BACKTRACK' verdict instead of freezing your browser. 🆚 Why this over the alternatives ✓ Unlike regex101.com, your patterns and test text stay local - never sent to a server ✓ Unlike VSCode regex - which only runs the JS engine in find/replace - this gives you saved patterns, a library, explanations, and a cheatsheet in one popup ✓ Unlike RegExr, no signup required for the free tier and the explanation walker is fully offline ✓ Unlike CLI tools like ggrep -P, you get a GUI with live highlighting and capture group inspection without leaving the browser 🛡️ Security Manifest v3. Zero remote code. No external CDN dependencies at runtime. No host permissions for arbitrary websites - only peakproductivity.online for license verification. Every release is audited by the lint-remote-code tool before submission. All evaluation logic ships inside the bundle. ❓ Frequently asked questions Q: Does it work offline? A: Yes. Live matching, replace preview, the cheatsheet, the AST explanation walker, and the catastrophic backtracking detector all run 100% locally. Only license verification and growth pings need the network, and both gracefully degrade. Q: Which regex flavor does it use? A: JavaScript regex (ECMAScript 2018+) for live evaluation. The cheatsheet and explanation walker note where syntax differs from PCRE / Python / Go so you can spot portability issues. Q: Is my regex sent anywhere? A: No. Patterns and test strings are processed in your browser. License checks send only a random device ID. Q: How big a test string can I throw at it? A: Tested cleanly up to 1MB. Beyond that, the live highlighter switches to debounced mode to keep the popup responsive. Q: What is the difference between Monthly ($2.49) and Lifetime ($8.99)? A: Same Pro features, different commitment. Lifetime pays for itself in four months and is the best deal if you regex more than once a week. Q: Can I get a refund? A: Within 30 days of purchase, yes. Email support and we will refund without questions. 🚀 Get started Install the extension, pin it to your toolbar, paste your first pattern, and watch the matches light up. Regex Tester Pro is the kind of tool you wish you had installed three years ago. Every senior engineer eventually has 'their regex tab', this one stays a click away in your browser, and it remembers what you saved.