Which regex flavor does this target?
JavaScript-style regular expressions, run with the RegExp object's global flag.
Developer Tools
Test a JavaScript Regular Expression
Test a JavaScript regular expression against sample text and see every matched substring, right in your browser.
What this test actually shows you
Enter a pattern and sample text, and this tool runs `input.match(new RegExp(pattern, "g"))` and shows the resulting array of matched substrings as formatted JSON. The regex always runs with the global flag only — there's no toggle for case-insensitive (i), multiline (m), or other flags, so if your pattern needs one of those, you'll need to build it into the pattern itself or test elsewhere.
The output is the list of matched text, not capture groups broken out separately, not match positions, and not a find-and-replace preview — it answers "what does this pattern match" rather than "what would this pattern replace it with."
Workflow at a glance
Use this quick flow to understand where the tool fits in your work and what to review before relying on the output.
Review checklist
Before
Prepare both a typical example and a few deliberately tricky edge cases to test against.
After
Confirm the pattern doesn't match unintended text as well as correctly matching what you expect.
When to test a pattern before shipping it
Use it to quickly check whether a JavaScript regex pattern matches the text you expect before it goes into a validation function, a search feature, or a text-cleanup script.
Who tests regex patterns
Frontend developers
Test a validation pattern (email, slug, ID format) against sample inputs before adding it to a form.
Backend developers
Check a pattern against sample log lines or data before using it in a search or filter.
QA testers
Verify a regex behaves as expected across a set of edge-case inputs.
Anyone debugging an unexpected match
See exactly what a pattern is matching (or not) against real sample text.
What the output includes — and what it doesn't
Live match testing
Shows matched substrings as soon as you enter a pattern and sample text.
Global flag only
The regex always runs with the g flag — no toggle for case-insensitive or multiline matching.
JSON array output
Matches are shown as a formatted array of matched strings.
JavaScript regex syntax
Targets the RegExp syntax JavaScript itself uses, not other regex flavors like PCRE or Python's re.
Testing a pattern step by step
- 1Paste the sample text you want to test against.
- 2Enter the regular expression pattern.
- 3Review the array of matched substrings in the output.
- 4Adjust the pattern until it matches the right text without catching too much.
Where regex testing fits into a workflow
Testing email, slug, or ID validation patterns.
Finding specific values inside logs or copied output.
Preparing text cleanup rules before using replace operations.
Debugging why a JavaScript regex does not match expected input.
Where your text and pattern go
The regex test runs directly in your browser using JavaScript's native RegExp — nothing you enter is sent to a server.
Getting a pattern that matches correctly
- Build case-insensitivity into the pattern itself (or test with both cases of sample text) since there's no separate flag toggle here.
- Test with realistic edge cases, not just the ideal input, to catch a pattern that's too greedy or too narrow.
- If you need to see a replace result rather than just matches, test that step in your actual code or editor.
- Keep patterns as specific as needed but no more — overly broad character classes are the most common cause of unexpected matches.
Regex testing mistakes to avoid
Expecting a flags toggle
The regex always runs with just the global flag — case-insensitive or multiline behavior needs to be built into the pattern.
Testing only the happy path
A pattern that matches the obvious example can still fail on edge cases — test a few deliberately tricky inputs too.
Using regex for structured formats like HTML
A parser is usually a better fit than regex for nested or structured markup.
Assuming this previews a replace operation
The output shows matched substrings only, not what a find-and-replace would produce.
Before this pattern reaches production code
Regex Tester is a fast way to confirm what a JavaScript pattern actually matches before it reaches real code. For flag variations or a replace preview, you'll still want to test directly in your editor or runtime.
Need hands-on help?
Get help with documents, SEO, content, or website fixes
Use this tool for quick work. If you need a real file prepared, a page reviewed, or a website issue fixed, send the URL and describe the problem.
FAQ
Regex Tester FAQ
Answers for using Regex Tester on I Love Tool XYZ.
Can I toggle case-insensitive matching?
Not directly — build it into the pattern itself, since only the global flag is applied here.
Does this show a replace preview?
No, only the list of matched substrings — not what a find-and-replace would output.
Should regex parse HTML?
Usually no. Use a parser for structured HTML; regex is better for simpler text patterns.