Build extraction rules
Test named-looking pieces such as order codes, tags, dates, or headings before putting a pattern in application code.
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Regex Tester
Test JavaScript regular expressions in your browser. View matches, capture groups, flags, indexes, and syntax errors against sample text.
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See matches, groups, and common errors. Your result updates in the current tab as you work.
Regex Tester
See matches, groups, and common errors. Nothing you enter here is uploaded or stored.
Matches and preview
1. team@example.com [index 8]
2. support@sovrancode.dev [index 28]
--- Test details ---
Pattern: /\b[a-z]+@[a-z]+\.[a-z]{2,}\b/gi
Matches: 2WHAT IT DOES
Useful when a small detail is blocking the next step.
Regular expressions are compact programs for matching text. They can validate a small pattern, extract structured pieces, or become unreadable when they attempt to parse an entire language. This tester runs a JavaScript regular expression against your sample text and reports each match, position, and capture group.
Understand capture groups
See exactly which parenthesized groups are returned for every match.
Try flags deliberately
Compare case-insensitive, global, multiline, or Unicode behavior against a real sample.
WORKED EXAMPLES
See the exact decision the tool can help you make.
These examples are specific to Regex tester. Replace their values with your own, then use the result as a clue—not as a substitute for application validation.
Extract an issue key
Release notes contain project references such as SC-204 and API-19.
INPUT
pattern: ([A-Z]{2,8})-(\d+)
text: Fixes SC-204; follows API-19.RESULT
Match 1: SC-204 → group 1: SC, group 2: 204 Match 2: API-19 → group 1: API, group 2: 19
The outer parentheses make each piece available to application code, while the global flag finds every occurrence.
Avoid matching inside a longer word
You only want the word cat, not catalog or educate.
INPUT
pattern: \bcat\b text: cat catalog educate
RESULT
Match: cat at index 0
Word boundaries are useful for word-like text, but test punctuation and non-Latin text because boundary behavior is engine-specific.
HOW TO USE IT
Three deliberate steps.
Use the result to make a decision in your code or content, not merely to produce another value to copy.
- 01
Enter the pattern only
Do not include leading and trailing slash delimiters; enter flags in the separate field.
- 02
Use representative text
Include expected matches, near misses, and an edge case so a pattern is not accidentally too broad.
- 03
Inspect every match
A match that looks right once can still capture the wrong text or skip a later occurrence.
Regex does not validate every real-world concept
An email-shaped string is not proof an inbox exists, and a date-shaped string is not proof it is a valid calendar date. Pair pattern matching with domain validation where correctness matters.
The m flag changes what ^ and $ mean across lines. The s flag allows dot to cross line breaks. The u flag changes Unicode interpretation. Make flags part of the test case rather than an afterthought.
/^todo$/m.test("done\ntodo\nnext") // true
/^todo$/.test("done\ntodo\nnext") // falseCOMMON PITFALLS
Use the result without creating the next bug.
Each tool is deliberately narrow. These are the mistakes most likely to appear when its output is copied into a real product without checking the surrounding constraint.
Adding the global flag and calling .test repeatedly on the same RegExp.
Why it matters: JavaScript advances lastIndex for global regexes, which can make alternating calls appear to fail.
Better approach: Use a non-global expression for a yes/no test or reset lastIndex before each call.
Writing a single giant pattern for nested or recursive data.
Why it matters: It becomes fragile, hard to review, and can have poor performance.
Better approach: Use a parser for structured formats and keep regexes focused on bounded tokens.
FAQ
Questions worth answering before you rely on the result.
These tools help with bounded client-side work. Production decisions still need the validation, review, and authorization appropriate to your application.
01Which regex flavor does this use?
It uses the JavaScript RegExp engine available in your browser. Syntax and flags can differ from PCRE, Python, Ruby, or database regex engines.
02Why are there no matches?
Check escaping, case, whitespace, flags, and whether \b boundaries fit punctuation in the sample. Start with a smaller literal pattern, then add constraints.
03Should I use regex to parse HTML or JSON?
No. Use an HTML parser or JSON parser for nested structured formats. Regex is best for bounded text patterns.
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