Regex Tester
Try a regular expression on your text as you type and see every match highlighted. Each match lists its position and capture groups, and a replacement like $1 shows the result before you ship it. Runaway patterns are stopped after one second so the browser never freezes.
Paste here
Result
Base64 · URL
Decode a JWT
The signature is not verified — that needs the key, and pretending otherwise is worse than not doing it. This only decodes the contents.
Hash
MD5 is not included. Browsers don't offer it, and it should not be used for anything new.
UUID · time
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Passwords
Color conversion
- HEX
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- RGB
- —
- HSL
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Contrast ratio (WCAG)
This is how text looks in that pair
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Color palettes
Page details
Tags to paste
Paste code
Result
Only comments and whitespace are removed. Names are left alone — renaming without scope knowledge silently breaks code, and it does not make the code unreadable anyway.
Paste HTML
The pasted code is never executed and never leaves your browser — it is only read.
Result
Units
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Pyeong ↔ square meters
1 pyeong is 400/121 m² (about 3.3058 m²). Type in either box and the other updates.
Apartment exclusive area
Apartment sizes quoted in pyeong in Korea usually mean supply area (exclusive area plus stairs and hallways), so they're larger than the exclusive area converted.
Year · sexagenary cycle
Japanese era (wareki) ↔ Gregorian
Short forms like R1.5.1 or H31 work. In a year when the era changed, enter the full date to get a single answer.
Number to Korean words
Used when writing amounts on contracts and quotes — the number and the words together make tampering harder.
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Korean name romanization
Follows the Revised Romanization of Korean. Sound changes inside a given name aren't reflected, as the standard requires. A passport's English name is hard to change, so if you already use a spelling, keep it.
Enter the name in Hangul.
Naming style
Internationalized domain
See the form a non-ASCII domain is actually registered as (xn--). Uses the browser's own standard conversion.
Regular expression
Result
After replacement
Original
Revised
What changed
YAML support covers the widely used subset — where anchors, tags, or multiple documents appear, this stops and says so rather than misreading them.
Result
Cron expression
Next runs
Computed in this browser's time zone. Server cron usually runs in UTC, so these times can differ from what your server will do.
About this tool
How to use it
- 1 Type the pattern. Leave out the surrounding slashes.
- 2 Tick the flags you need (g, i, m, s, u) and paste the text to test.
- 3 Check the highlighted matches and groups, and type a replacement to preview it.
Good to know
- The page audit reads HTML you paste — use the Link checker to follow a link
- YAML support covers the widely used syntax only
- JWT decoding unpacks the contents; it does not verify the signature
Frequently asked questions
Which regex flavor is this?
JavaScript (ECMAScript). Syntax JavaScript lacks, like possessive quantifiers (a++) or atomic groups, shows an error.
It says the pattern didn't finish within a second.
Nested repetition like (a+)+ blows up on slightly longer input. Rewrite it so the repeats don't overlap.
How do I use groups in the replacement?
Use $1, $2 for numbered groups, $<name> for named groups and $& for the whole match.
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Estimate how many tokens your text is and what each model would cost. Your text never leaves the browser.