Regular Expression Tester

Test, validate, and learn regular expressions with real-time pattern matching

Regular Expression

Pattern:

/ /

Flags:

g Global i Ignore Case m Multiline s Dot All

Test String:

Quick Patterns:

Test Results

Match Status: Ready

Highlighted Matches:

Test results will appear here...

Pattern Explanation

Enter a regex pattern to see its explanation here...

Find & Replace

Replacement String:

Replaced Text:

Common Patterns

Character Classes

\d - Digits (0-9)

\w - Word characters (a-z, A-Z, 0-9, _)

\s - Whitespace characters

. - Any character (except newline)

Quantifiers

* - Zero or more

+ - One or more

? - Zero or one

{n,m} - Between n and m

Anchors

^ - Start of string

$ - End of string

\b - Word boundary

Common Use Cases

Email Validation

Validate email address format

^[^\s@]+@[^\s@]+\.[^\s@]+$

Phone Numbers

Match various phone formats

^\+?[\d\s\-]{10,}$

Password Strength

At least 8 chars with mixed case

^(?=.*[a-z])(?=.*[A-Z])(?=.*\d).{8,}$

URL Extraction

Find URLs in text

https?:\/\/[^\s]+

Features

🎯 Real-time regex pattern testing
🔍 Visual match highlighting
📝 Pattern explanation and breakdown
🔄 Find and replace functionality
📚 Common regex pattern library
🏷️ Capture group visualization

Use Cases

✅ Form validation patterns
🔍 Text parsing and extraction
📧 Email and URL validation
🔐 Password strength checking
📞 Phone number formatting
🎓 Learning regular expressions

6. Days Until

What it does: "Days Until" calculates how many days remain until a target date (a birthday, holiday, event). It is essentially a date-difference from today to a future date but often presented with friendly copy and optional recurrence handling for yearly events.

Features

Support recurring yearly events: if the target date this year already passed, compute days until the date next year.

Offer both exact days and a human-friendly format like "2 months and 5 days".

Countdown formatting: allow users to toggle between days-only, weeks + days, or months + days.

Example: Today is 2025-09-24 — Days until 2025-12-25 (Christmas) = 92 days.

Putting it all together — Building reliable web calculators

Here are practical tips for developers and product managers building these tools on websites and mobile apps:

Use tested date libraries. Rely on battle-tested libraries (like Luxon, date-fns, or the native Intl APIs) rather than hand-rolled date math. They handle leap years, daylight saving time, and locale formats.

Validate user input. Provide clear error messages, accept multiple formats, and sanitize all numeric input to avoid parsing errors (commas vs dots in decimals).

Provide educational context. For BMI and loan calculators, include short notes about limitations (BMI) and fees/assumptions (loans) so users understand what the outputs mean.

Accessibility. Make forms keyboard-friendly, support screen readers, and provide visible focus states. Add aria-live regions to announce results to screen reader users.

Performance and privacy. Calculations should occur client-side where possible to reduce latency and avoid storing sensitive input like birth dates or financial figures on servers unless explicitly needed.

Internationalization (i18n). Respect local number and date formats, offer metric and imperial units, and translate messages for broader reach.

Sample HTML form (simplified)

<form id="percentage-form"> <label>Base: <input name="base" type="number" step="any" /></label> <label>Percentage: <input name="percent" type="number" step="any" /></label> <button type="submit">Calculate</button> </form>

Attach client-side JS to compute results instantly and show them inside an accessible result container.

Design & SEO considerations

These calculator pages are highly searchable. Follow these quick SEO tips:

Provide clear titles and meta descriptions (as used in this page).

Use structured data (Schema.org) where appropriate — for example, FAQ schema if you include common questions about the calculators.

Offer shareable results or a printable summary for users who want to save calculations or share with advisors.

Include internal links between calculators (users often transit between percentage calculators, loan calculators and BMI pages).

Conclusion

Age, Percentage, Loan, BMI, Date Difference, and Days Until calculators are simple but powerful tools that deliver immediate value. When implemented carefully — with correct formulas, clear UX, accessibility, and privacy considerations — they can significantly improve user engagement and trust. Developers should prefer reliable libraries for date and numeric handling, clearly document assumptions, and provide helpful explanations so users can understand and act on their results.

If you’d like, I can also provide ready-to-use JavaScript snippets for any of the calculators above (for example, a full amortization table script for the Loan Calculator or a BMI widget with unit toggles). Tell me which one you want first and I’ll include a copy-pasteable implementation.

Regular Expression Tester