freesabaiRegex tester
Type a regular expression and some test text and see where it matches. Matches are highlighted in the text and listed in a table with the groups they capture. Try a replacement with $1. If a regex runs so long that it would hang (ReDoS), the tool stops it within 1 second and the page never freezes. It runs in your browser.
This tool needs JavaScript. If you still see this after a few seconds, JavaScript is switched off in your browser or the page did not load completely: turn JavaScript on or reload the page.
How to use it
- Type the regex between the / / and choose the flags (
g, to find every match, is on by default), or choose one from "Examples". - Type or paste the test text. Matches are highlighted at once, and the table below gives the position and captured groups of each.
- Tick "Try a replacement" and give the replacement (
$1is group 1,$<name>a named group) to see the whole text after it.
Frequently asked questions
My regex makes the browser hang. Why?
Some regexes, such as (a+)+$, try every way of splitting the characters when the text does not match, and the time doubles with each extra character (called catastrophic backtracking, or ReDoS). In this tool the matching runs in a background worker, and if it takes more than 1 second it is stopped. Your page does not freeze, and you are told it is probably ReDoS.
Can I use regexes from other languages (Python, PHP, Java)?
This tool uses the browser's engine, so the syntax is JavaScript's. Much is the same, but some things differ: a named group is written (?<name>…) in JavaScript, not Python's (?P<name>…), and JavaScript has no inline flags such as (?i). The result is exactly right for JavaScript code; for other languages, check again.
How do I match Thai letters?
Use the range [\u0E00-\u0E7F]+, which covers Thai consonants, vowels and tone marks. Try the "Thai letters" example. Note that JavaScript's \w and \b do not know Thai letters (they count only a-z, 0-9 and _). To match letters of every language, use the u flag with \p{L} and \p{M}.
Good to know
- Flags:
gevery match,iignore case,m^ and $ per line,s. matches line breaks,uUnicode mode (\p{…} and emoji),ysticky,dgroup positions. - At most the first 1,000 matches are listed, but the total is counted.
- Test text over 1 MB is cut to its first 1 MB.
Your data stays on your device
Everything runs in your browser. What you type, paste or open is not sent to freesabai's servers or anyone else's, and is not kept in the browser: close the page and it is gone. The site only counts how many times this page was opened and how many times someone copied or saved a result (never what was pasted or the result, and you can switch the counting off in the footer; see the privacy policy).
Report a problem or suggest an idea
Found a bug, or want this tool to do more? Tell us on the feedback page. No sign-up.
Other developer tools
JSON and data
- JSON formatter and validatorFormat, minify and validate JSON, find the error, fold it into levels
- JSON to YAML converterTurn JSON into YAML, key order kept, nothing leaves your device
- YAML to JSON converterTurn YAML into JSON, and find the line where the YAML is wrong
- JSON to CSV converterTurn a JSON list into CSV for Excel, Thai text included
- CSV to JSON converterTurn CSV into JSON, any separator, quoted fields handled
- CSV viewerOpen a CSV file as a table, sort a column, search, no spreadsheet needed
- Text and JSON diff checkerSee what changed between two texts, side by side or unified, with word highlights
Encoding, hashes and tokens
- Base64 encode and decodeBase64 for text (Thai and UTF-8), URL-safe, and files to and from Base64
- Hash generator: MD5, SHA-256, HMACHash text or files with MD5, SHA-1, SHA-256, SHA-512 and HMAC, and verify a checksum
- JWT decoderRead the header and payload of a JWT, with times you can read (decode only, no signature check)
- URL encode and decodePercent-encode or decode a link, Thai in URLs included, and take a URL apart
- HTML entities encode and decodeTurn special characters into & < > " and back
Generators
Time, numbers and colour
- Unix timestamp converterConvert a timestamp (seconds or milliseconds) to a date and back, with time zones
- Cron expression explainerRead a cron expression in plain words and see its next 5 runs
- Number base converterConvert between binary, octal, decimal and hex, and do bitwise AND, OR, XOR and shifts
- Colour converter: HEX, RGB, HSLConvert a colour between HEX, RGB and HSL, or pick one by eye
- Colour contrast checker (WCAG)Check the contrast between text and background colours for WCAG AA and AAA
Text and code
- Regex testerTry a regular expression, see matches and groups, protected from regexes that never finish
- Markdown previewType Markdown and see it rendered at once, safely, with embedded scripts never run
- Character, word and line counterCount characters, words (Thai too), lines, sentences, paragraphs and reading time