How to use this tool
- Enter a JavaScript regular expression pattern without surrounding slashes.
- Toggle flags such as global, ignore case, multiline, dotAll, or unicode.
- Review matches, groups, indexes, and replacement output.
Developer Utility
Regex Tester
Test JavaScript regular expressions locally, inspect matches and capture groups, toggle flags, and preview replacement output without uploading text.
Regex examples and workflows
Use this tester for logs, API payloads, form validation, find-and-replace, and capture-group debugging.
Real examples
- Find all email-like strings in copied logs.
- Capture URL slugs from route paths.
- Preview a replace operation before changing source text.
Common use cases
- Debug frontend validation patterns.
- Extract IDs, timestamps, or status codes from logs.
- Test capture groups before using them in JavaScript code.
Sample input/output
- Pattern:
([a-z]+)@example\.com - Text:
ada@example.comandlin@example.com. - Output: two matches with group 1 values
adaandlin.
Common errors and fixes
- Invalid regular expression: check unclosed groups, brackets, or escapes.
- No matches: verify flags, anchors, whitespace, and case sensitivity.
- Unexpected replacement: use
$1,$2, and named groups carefully.
Edge cases table
| Case | What to check |
|---|---|
| Multiline anchors | Use m when ^ and $ should apply per line. |
| Dot matches newline | Use s when . should cross line breaks. |
| Global matching | Use g to list all matches instead of only the first one. |
Edge cases / errors
- Catastrophic backtracking can freeze very large inputs.
- Lookbehind support depends on the browser JavaScript engine.
- Regex syntax differs between JavaScript, PCRE, Python, and RE2.
Related workflow
- Test patterns on decoded text from Base64 Encoder / Decoder.
- Extract values from formatted payloads with JSON Formatter / Validator.
- Decode URL samples first with URL Encoder / Decoder.
Related developer tools
Use these tools around regex debugging and text extraction workflows.
JSON Formatter / Validator
Format JSON before extracting values or testing patterns.
URL Encoder / Decoder
Decode URLs before matching query strings or route patterns.
Base64 Encoder / Decoder
Decode text payloads before testing regular expressions.
Timestamp Converter
Convert matched Unix timestamps into readable dates.
Regex Tester FAQ
Practical details about JavaScript regex testing.
Does this upload my text?
No. Pattern matching and replacement preview run locally in your browser.
Which regex flavor is supported?
This page uses JavaScript RegExp syntax, matching modern browser behavior.
Can I inspect capture groups?
Yes. Each match row lists captured groups when the pattern contains parentheses.
Can I preview replacement text?
Yes. Enter replacement text and run the pattern to preview the replaced output.