Regex Tester & Generator
Test, explain, generate, debug, visualize and optimize regular expressions instantly. The complete regex platform — with AI-style explainer, language code generator, debugger, complexity analyzer and 100+ ready-made patterns.
Quick Answer
Regex Studio is a free online regular expression tester, generator, explainer and debugger. Paste a regex pattern and test string to see live matches, plain-English explanations, step-by-step execution, complexity scoring and ready-to-paste code for Java, JavaScript, Python, C#, Go, PHP, Rust, Kotlin and Ruby — all running locally in your browser.
Live Regex Tester
Analysis
Human-readable, token-by-token explanation of your pattern.
Visual flow of the regex execution graph (anchors, classes, groups, quantifiers).
Token-by-token execution walkthrough against the first non-empty input line.
Pinpoints where matching failed and which character broke the match.
Suggestions to make your pattern shorter, faster and safer.
Sample strings generated from your pattern.
Matching examples
Non-matching examples
Plain-English description of what the regex matches.
Reverse Regex
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Regex Generator
Describe what you want to match in plain English. The generator recognizes 50+ common intents (email, URL, phone, UUID, JWT, IPv4/IPv6, dates, hex color, credit card, ZIP, password rules, and more).
Matches a valid email address: local part with letters, digits and common symbols, followed by @, domain and a TLD of 2+ letters.
Language Code Generator
Idiomatic regex code for your pattern in 9 languages — copy and paste straight into your project.
Regex Pattern Library
0 patternsNamed Groups
Use (?<name>...) to capture into a named group. Generator below wraps your pattern.
Flags Playground
Toggle flags on the tester above and see how each one changes matching.
gGlobal — find all matches, not just the first.iIgnore case — A matches a.mMultiline — ^ and $ match line boundaries.sDotall — dot (.) also matches newline.uUnicode — full Unicode escapes and surrogate pairs.ySticky — match from lastIndex only.Interactive Cheat Sheet
Learning Mode
Challenges
Regex Interview Questions
Validation Rules
Drop-in validation snippets generated from your current pattern.
JSON Schema
A JSON Schema fragment using your pattern as a string constraint.
Saved Patterns
No saved patterns yet — hit the Save button in the tester to bookmark one.
Key Takeaways
Anchor when you can
Use ^ and $ for full-string validation — much faster and fewer false positives.
Avoid nested quantifiers
Patterns like (a+)+ can backtrack catastrophically — flatten them or use possessive quantifiers.
Prefer named groups
(?<year>\d{4}) is self-documenting and survives reordering better than numeric groups.
Use character classes
\d, \w, \s are shorter than [0-9], [A-Za-z0-9_], [ \t\n].
Lookarounds are powerful
Zero-width assertions (?=...) and (?<=...) let you match without consuming.
Test with edge cases
Empty strings, Unicode, leading whitespace, newlines — the test data generator above seeds these for you.
Common Use Cases
Form validation
Email, phone, ZIP, password strength — client and server-side.
Log parsing
Extract timestamps, IPs, status codes from access logs.
Secret scanning
Detect JWTs, API keys and credentials in source code.
Code refactoring
Rename APIs and migrate syntax across a codebase safely.
ETL & data cleaning
Normalize phone numbers, currencies, dates and identifiers.
Security rules
WAF rules, input sanitization, deny-list patterns.
Troubleshooting
My pattern matches nothing — what's wrong?
Check your anchors. ^ and $ require the entire string (or line in multiline mode) to match. Remove them, or enable the m flag to match per line.
Why does . not match newlines?
By default, . matches any character except newline. Enable the s (dotall) flag, or use [\s\S].
My regex hangs the browser.
You likely hit catastrophic backtracking — open the Complexity tab. Replace nested quantifiers like (a+)+ with a+, or use atomic groups in PCRE-flavored engines.
Group 1 is empty but the match isn't.
You used a non-capturing group (?:...). Switch to (...) to capture, or name it with (?<name>...).
Unicode characters don't match \w.
\w only covers ASCII [A-Za-z0-9_]. Use the u flag and Unicode property escapes like \p{L}.
Frequently Asked Questions
What is a regular expression?
A regular expression (regex) is a compact pattern syntax for matching, searching and replacing text. It is built into nearly every programming language and tool — JavaScript, Java, Python, grep, sed, vim, IDEs and databases all use compatible flavors.
Which regex flavor does this tester use?
The live tester uses the JavaScript (ECMAScript) engine, which is very close to PCRE. The Language Generator emits idiomatic, copy-paste-ready code for Java, Python, C#, PHP, Go, Rust, Kotlin and Ruby — each with its compile/match calls.
Is my data safe?
Yes. Everything runs locally in your browser. No patterns or test input ever touch our servers.
What is catastrophic backtracking?
It's an exponential slowdown caused by ambiguous, overlapping quantifiers (typically nested quantifiers like (a+)+). The Complexity tab detects risky shapes and the Optimizer suggests safer rewrites.
Can I share a pattern with a teammate?
Yes — click Share in the tester. The URL encodes the pattern, flags and test input so the page reloads in the same state.
Do you store my saved patterns?
Saved patterns live in your browser's localStorage only. Use Export JSON to back them up or move them between devices.