Announcing jto/validation 2.0

The new version of my validation library is out. After a few years in production, it was time for it to undergo a massive update.

What's jto/validation again ?

jto/validation is a library originally born to replace play-json validation features. It aimed to generalize the library to support other data formats. jto/validation never made it to Play because it was thought to be to big a leap (at least for Play 2.x).

Today, the library supports JSON (both play-json, json4s, and "native"), play forms, XML and CSV. It is also easily extensible to any data format.

Why 2.0 ?

After using v1.x for years, we had a pretty clear idea on how to improve it. Here's are the most important evolutions:

  • We got rid of play-functional, and replaced it with cats. Cats is well written, well maintained, well documented, complete and sound, and is a great fit for us.
  • Since jto/validation is decoupled from Play, it now supports Scala.js. You can now write Rules and Writes, and share them between the server and the browser.
  • The library now has a proper package name, and does not steal Play's anymore.
  • jto/validation 2.0 supports Play 2.5.x (via the dedicated playjson module)

Other improvements

  • Tests are now automatically run on
  • Code coverage is now measured, and published automatically on We'll give the library an even better test coverage in the future releases.

How do I use It ?

The project's README should provide everything needed to start

Where's the doc ?

Version 2.0 comes with an all new and shiny gitbook, featuring a live example in the Scala.js section. That's right, you can try the library directly in your browser!

Is it backward compatible with 1.x ?

Almost ;) You'll have to do a (tiny) bit of work to migrate from 1.x to 2.0. Fear not, the migration has been tested, and the required steps documented here. Migrating should take a few minutes at most. The compiler will also guide you through the migration with deprecation warnings giving clear indications on how to migrate


Feedbacks (positive and negative), bug reports and pull requests have always been more than welcome. Come talk with us on github, or in the gitter channel.


The library now has a second maintainer: Olivier Blanvillain. Credits for this new version should go to him. He, amongst other things, added Scala.js support, created the git book and replaced play-functional by cats.

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