git clone ''

(ql:quickload :venantius.ultra)


Hey, you know who has two thumbs and strong opinions? That's right, it's me.

Ultra is a Leiningen plugin for an absolutely kick-ass development environment.

I've written a blog post describing Ultra in greater depth here.

Ultra is the rare piece of essentially “finished” software. I've ironed out most of the bugs, and don't plan on adding much in the future. In other words: it's not unmaintained, it's just done.


To install Ultra, just add the following to your ~/.lein/profiles.clj

{:user {:plugins [[venantius/ultra "0.6.0"]]}}


Lein 2.9.0
Clojure 1.7+

If you want to use something older, see

ClojureScript Support

At the moment, Ultra doesn't have ClojureScript support at the REPL. The relevant upstream issue to track work on this is; from there, Whidbey will need to be updated, and then Ultra will be able to consume the changes.


For a detailed list of features, check out the wiki. Here's the highlight reel:

A colorized REPL! colorized repl

Syntax-highlighted source! colorized source

Clearer test output! test output demo

Better stacktraces! test stacktrace demo


All of the above features are enabled by default, but can be turned off by setting a false flag in your profile. If you wanted Ultra to essentially no-op, your configuration map would look like this:

{:ultra {:repl         false
         :stacktraces  false
         :tests        false}}

REPL Configuration

Ultra uses Whidbey as its pretty-printing engine, and supports all of Whidbey's configuration flags.

{:ultra {:repl {:width 180
                :map-delimiter ""
                :extend-notation true
                :print-meta true

Number of characters to try to wrap pretty-printed forms at.


If true, metadata will be printed before values.


Print maps and sets with ordered keys. Defaults to true, which will sort all collections. If a number, counted collections will be sorted up to the set size. Otherwise, collections are not sorted before printing.


The text placed between key-value pairs in a map.


The text placed between a map key and a collection value. The keyword :line will cause line breaks if the whole map does not fit on a single line.


If set to a positive number, then lists will only render at most the first n elements. This can help prevent unintentional realization of infinite lazy sequences.

Using CIDER alongside Ultra

Projects which extend the Clojure REPL will conflict with each other; a middleware which modifies REPL print output will break the assumption of another middleware expecting unmodified Clojure output. Specifically, Ultra and CIDER collide on certain test result values (#79).

Use either CIDER or Ultra, but not both. Configure cider-jack-in to skip the Leiningen user profile, and therefore skip using Ultra, in .emacs:

; Skip :user section of ~/.lein/profiles.clj when using cider-jack-in.
(setq cider-lein-parameters
      "with-profile -user repl :headless :host localhost")

If you have a lein user profile intended to alter CIDER's behavior, consider these options:

  1. Declare a separate profile and name it in with-profile -user,YOURPROFILE in the Emacs cider-lein-parameters variable.
  2. Configure CIDER's cider-jack-in-lein-plugins variable.

CIDER added variables:

Running project tests may cause the CIDER REPL to hang (#79) when using cider-connect (as opposed to cider-jack-in) with an existing lein repl which is running Ultra.


Please open an issue here before submitting pull requests; I prefer to have documentation and consensus that either of our time will be well spent by working on it. When opening an issue – particularly for bugs – please refer to

Bug fixes and code cleanup are always appreciated and won't get too much pushback; new features will be held to a higher standard - this whole project is something of a massive exercise in ego, after all.


…or, why didn't you just put all of this stuff in your ~/.lein/profiles.clj?

In short, my :user profile was starting to become bloated. It was difficult to tell whether plugins were interfering with each other, and my :injections key in particular was starting to look a little unwieldy.

At some point I realized I was up to my neck in alligators and that it was time to push things into a standalone repository.

Special Thanks

Ultra wraps, calls, or draws inspiration from the following libraries, and their owners and authors deserve credit for doing most of the hard work.


In some cases, I've borrowed code snippets from libraries above and re-written them. Where that is the case, the Copyright of the original author[s] remains in effect. Any modifications to their code, as well as all original content, is Copyright © 2019 W. David Jarvis.

Distributed under the Eclipse Public License 1.0, the same as Clojure.