Key capabilities
- Live matching
- Capture groups
- Replacement preview
- Local processing
Regex Tester
Debug regular expressions locally in the browser with flags, match highlighting, capture groups, named groups, and replacement preview.
Regular expression
Enter the pattern without wrapping slashes.
Matched
Test text
Paste logs, API responses, or plain text. Matches are highlighted on the right.
3 / 81
Match highlight
Shows matches live with the current flags.
GET /api/users?id=42 200 18ms
POST /api/login 401 33ms
GET /assets/app.js 304 4ms
Rule library
Save useful patterns, replacements, flags, test text, and test cases for one-click restore and validation later.
0 rules
0 results
0 selected
Pattern insights
Detects the current pattern structure, capabilities, and possible risks.
Capture groups
Info4 capture groups were detected for export, replacement, and downstream processing.
Alternation branches
Info| branches were detected. A broad branch placed first can consume text before later branches are tried.
Performance risk
Combines static risk checks with a lightweight benchmark.
A lightweight performance test will run after the page finishes loading.
Token explanation
Breaks down key pattern segments in order.
(Group0-1Starts a capturing group that can be referenced in matches and replacements.
GETLiteral1-4Matches this text literally.
|Branch4-5Branch matching: either side may satisfy the pattern.
POSTLiteral5-9Matches this text literally.
)Group9-10Ends the current group.
\sEscape10-12Matches one whitespace character.
+Quantifier12-13Repeats the previous segment one or more times.
(Group13-14Starts a capturing group that can be referenced in matches and replacements.
\/Escape14-16Matches an escaped special character or control sequence.
\SEscape16-18Matches one non-whitespace character.
+Quantifier18-19Repeats the previous segment one or more times.
)Group19-20Ends the current group.
\sEscape20-22Matches one whitespace character.
+Quantifier22-23Repeats the previous segment one or more times.
(Group23-24Starts a capturing group that can be referenced in matches and replacements.
\dEscape24-26Matches one digit character.
{3}Quantifier26-29Repeats the previous segment according to {3}.
)Group29-30Ends the current group.
\sEscape30-32Matches one whitespace character.
+Quantifier32-33Repeats the previous segment one or more times.
(Group33-34Starts a capturing group that can be referenced in matches and replacements.
\dEscape34-36Matches one digit character.
+Quantifier36-37Repeats the previous segment one or more times.
msLiteral37-39Matches this text literally.
)Group39-40Ends the current group.
Match details
12 capture groups detected.
3
#1 · 0-29
Start line 1, column 1End line 1, column 30
GET /api/users?id=42 200 18ms
Group 1
GET
Group 2
/api/users?id=42
Group 3
200
Group 4
18ms
#2 · 30-54
Start line 2, column 1End line 2, column 25
POST /api/login 401 33ms
Group 1
POST
Group 2
/api/login
Group 3
401
Group 4
33ms
#3 · 55-81
Start line 3, column 1End line 3, column 27
GET /assets/app.js 304 4ms
Group 1
GET
Group 2
/assets/app.js
Group 3
304
Group 4
4ms
Replacement preview
Supports $1, $2, and named group references.
3 changed linesChars +15
After checking the preview, write the replacement result back to the input.
Preview result
GET /api/users?id=42 -> 200 (18ms) POST /api/login -> 401 (33ms) GET /assets/app.js -> 304 (4ms)
Replacement diff
Shows only changed lines. Red is before, green is after.
Line 1
Before
GET /api/users?id=42 200 18ms
After
GET /api/users?id=42 -> 200 (18ms)
Line 2
Before
POST /api/login 401 33ms
After
POST /api/login -> 401 (33ms)
Line 3
Before
GET /assets/app.js 304 4ms
After
GET /assets/app.js -> 304 (4ms)
Test cases
Save multiple inputs and expected match counts, then validate the current regex in one run.
0 cases
When expected matches is blank, the current match count is used.
Pass rate
0%
Passed
0
Failed
0
Blocked
0
Capabilities
Live matching
Capture groups
Replacement preview
Local processing
Use cases
Debug log extraction rules
Validate form input patterns
Clean up text formats in batches
About Regex Tester
Test matches, groups, and replacement output. Debug regular expressions locally in the browser with flags, match highlighting, capture groups, named groups, and replacement preview. The core workflow is designed to run in your current browser.
Useful for
- Debug log extraction rules
- Validate form input patterns
- Clean up text formats in batches
Frequently asked questions
Is Regex Tester free to use online?
Yes. Regex Tester opens in a modern browser and does not require desktop software installation.
What is Regex Tester useful for?
Common use cases include Debug log extraction rules; Validate form input patterns.
Is my input or file uploaded?
The core processing workflow is designed to run locally in the browser. Key capabilities include Live matching, Capture groups, Replacement preview; account, comments, and anonymous analytics may still create normal site requests.
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