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RegEx Knife

RegEx Knife is an easy and useful tool for working with Regular Expressions. RegEx Knife is unique in how it allows you to highlight capture groups within a Regular Expression, edit them and immediately see the results. RegEx Knife also makes it easy to experiment with regular expression substitutions.

Version 2 retains the simplicity of the original RegEx Knife, with the added advantage that it works on your iPhone as well as your iPad.

RegEx Knife in the App Store

RegEx Knife 2

RegEx Knife blog posts

RegEx Knife privacy policy


  1. I would like to thank you so much for making this software available on the Apple appstore freely. I am currently learning about the regular expressions. Your software is an invaluable tool for learning how to use them properly and also how to refine a selection. Thumbs up!

  2. Karsten Karsten

    Hi, In the top Window i can not see the regex. It is possible to save the regex in a Other App?

    Best regards Karsten

  3. In the top Window i can not see the regex.

    This problem is caused by iOS 9. RegEx Knife 1.0.6 fixes this issue and is currently going through Apple app approval process. I expect it to appear over the next week or so.

    Is it possible to save the regex in a Other App?

    Other than Copy and Paste, there are no explicit save features. What would you like to see? Perhaps you can email me your ideas at

  4. Robert Robert

    Mark, can you make your regex keyboard available as additional keyboard for the ipad and not for only regex knife? I enjoyed the solution with the multiple values on 1 key and the swiping in the right directin to get one of the corner values. Very effective.

  5. Thats an interesting suggestion. I’ll look into it and see what can be done.

  6. Martin Steffens Martin Steffens

    Dear Mark,

    thank you a lot for this great free app. I really have to learn RegEx now…

    Greetings from Mannheim/Germany


  7. Maky Sy Maky Sy


    I like very much RegEx Knife. It is very practical for learning.

    Could you please tell me what RegEx engine it is using and what syntax is made available ?

    Best regards.

    Makha Sy

  8. Paul Laba Paul Laba

    Thanks for this great app! I expecially like your extended keyboard keys for entering or editing the regex expression, with its ‘directional swiping’ feature. Very clever! Apple could learn a thing or two…

    One wishlist item: Please support named groups in your substitution expression.

    Your app supports the syntax for named groups in the regex expression, like (?…), but doesn’t appear to support named groups in the substitution expression, like ${name}. It appears you only support numbered groups like $1, $2, etc. in the substitution expression.

  9. Shyam Shyam

    There’s a big in regex knife on iPhone 7+ & iOS 11.3

    If I close and open an file it’s showing like this can’t scroll up and see the expressions.

  10. ICU, the version provided by Apple with iOS.

  11. This is coming in my next maintenance release.

  12. I’m aware if this issue and I’ll resolve it in the next maintenance release.


    Hi~ Respectable Mark Alldritt:

    I am one of the RegEx Knife users and I really love this software. I can’t think of any convenient Regular Expressions assistance tool on the market, let alone it is free.

    I hope this software can continue to develop, for example: to increase the version of Mac OS X (data can be synchronized via icloud), or to allow the text entered by the software to support Chinese characters, and even to share each self-written sample to a friend or It is uploaded to the website for sharing, just like the codepen website (

    I am very happy to pay for the software, thank you for developing such a great app.


  14. Hi. Work is progressing once again on RegEx Knife. I’m currently working on fixing iOS ii issues and supporting named capture groups (introduced in iOS 11). Anyone interested in testing RegEx Knife is welcome to get in touch. I’ll need you email to send you a TestFlight invitation.

    Here’s the plan over the next while:

    2.0.1: fix some iOS 11 issues and support named capture groups
    2.1: move to CloudKit for expression storage to support multiple devices
    2.2: improve integration and sharing with other applications

  15. Shyam, you should receive a TestFlight invitation from Apple shortly.

  16. Sergey Sergey

    Please add iCloud sync for regexp

  17. Martin Martin

    Hi. Love regex knife but I found a bug:

    If you enter a \ in the substitution text box the app crashes. I need to reinstall to get it to work again. I’m on iOS 12. Let me know if you need anymore details.

  18. cliffclof cliffclof

    Second what martin says. Crash when \ is entered in sub.

    My regex search was: ^(?=.found).$\n

    That crashed the app in an unrecoverable state. Any way to reset the app to the home screen on launch from any previous state would resolve this? I can’t remember if i saved anything in your app or if that is possible. Rather not lose saved regex if you know what i mean.

  19. I’ve just submitted RegEx Knife 2.0.2 to Apple. An update should hopefully appear shortly.

  20. RegEx Knife 2.0.2 is now available.

  21. sunny sunny

    Regex knife version 2.0.2

    how to make text visible for sample text window? iOS 15.6.1 i reset all accessibility options pertinent to text

  22. sunny sunny

    i need help on following expression which doesn’t return anything on VERY</A)


    thanks ahead

  23. I use something like this to match simple HTML tags: <td\s.>\s(.)<\/td>

  24. The sample text field appears below the RegEx Field and the RegEx matching options. In an empty RegEx Knife expression, you’ll see the text ‘Enter Sample Tet Here’. Tap on that and then you can begin typing or pasting your sample text.

  25. hoojack hoojack

    Please support Chinese, thank you!

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