Regex Tester
Test regular expressions with live matching, capture groups, and flags. Supports JavaScript regex syntax.
0 matches
Recommended workflows
How to Use Regex Tester
- 1
Enter pattern
Type your regex pattern in the pattern field.
- 2
Set flags
Toggle flags: global (g), case-insensitive (i), multiline (m).
- 3
Enter test string
Paste or type the text you want to test against.
- 4
View matches
Matches are highlighted in real time. Capture groups are shown below.
Why Use a Regex Tester?
Regular expressions are one of the most powerful text processing tools available to developers, but writing them correctly without immediate feedback is notoriously difficult. A regex tester provides instant visual feedback as you type — showing exactly which parts of your test string match, what each capture group contains, and whether your pattern has syntax errors. This eliminates the slow compile-run-debug cycle of testing regex inside application code. Our regex tester uses the JavaScript (ECMAScript) regex engine, which is the same engine running in all modern browsers, Node.js, Deno, and Bun. Patterns you test here will work identically in your production JavaScript or TypeScript code.
Key Features
The tester provides real-time match highlighting as you type, with distinct colors for different capture groups so you can visually verify complex patterns. Toggle flags interactively: global (g) to find all matches, case-insensitive (i), multiline (m) to make ^ and $ match line boundaries, dotAll (s) to make . match newlines, and unicode (u) for proper Unicode handling. Named capture groups (ES2018) are fully supported and displayed with their group names. The error reporter explains exactly why an invalid pattern fails — whether it is an unterminated group, invalid quantifier, or unescaped special character. Match indices show the exact start and end positions within the test string.
Common Use Cases
Email validation, URL parsing, log file extraction, data sanitization, and search-and-replace operations are everyday regex tasks. Backend developers write regex for input validation in API routes — testing patterns against edge cases before deploying. Data engineers build extraction patterns for ETL pipelines, pulling structured data from semi-structured text. DevOps teams write regex for log parsing in tools like Logstash, Fluentd, and CloudWatch. Frontend developers use regex in form validation, ensuring phone numbers, zip codes, and credit card numbers match expected formats. Content teams use regex in CMS search-and-replace to fix formatting across thousands of articles simultaneously.
Regex Tips and Common Patterns
Start simple and build up — test each part of a complex pattern independently before combining them. Use non-capturing groups (?:...) when you need grouping but do not need the captured value, as they are faster. Prefer possessive quantifiers or atomic groups where supported to avoid catastrophic backtracking. Common patterns every developer should know: email (basic): [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}, URL: https?://[^\s]+, IPv4: \b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b, ISO date: \d{4}-\d{2}-\d{2}. Always test regex against both matching and non-matching inputs to verify you are not accidentally matching too broadly.
Frequently Asked Questions
Which regex flavor is used?▾
JavaScript regex (ECMAScript). This is the same syntax used in browsers, Node.js, and TypeScript.
Can I see capture groups?▾
Yes. Named and numbered capture groups are listed with their matched values.
Does it validate the pattern?▾
Yes. Invalid patterns show an error message with details about what went wrong.
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