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spec is a Clojure library to describe the structure of data and functions. Specs can be used to validate data, conform (destructure) data, explain invalid data, generate examples that conform to the specs, and automatically use generative testing to test functions.

For more information:

spec.alpha was released with Clojure 1.9 and can be found at This library is an evolution from spec.alpha as well as work towards several new features. Please note that alpha.spec is not 100% API-compatible with spec.alpha (although it is similar).

Namespaces to load:

(require '[clojure.alpha.spec :as s]
         '[clojure.alpha.spec.gen :as gen]
         '[clojure.alpha.spec.test :as test])

Also see: Differences from spec.alpha

Releases and Dependency Information

This library is a work in progress provided to gather feedback during development. Namespaces, apis, etc may change without warning. The HEAD may not always be stable (although it usually is).

During development, you can use the git dep to try alpha.spec:

clj -Sdeps '{:deps {org.clojure/clojure {:mvn/version "1.10.1"}
                    org.clojure/test.check {:mvn/version "0.9.0"} 
                    org.clojure/alpha.spec {:git/url "" 
                                            :sha "<SHA>"}}}'

Where the latest SHA can be found with:

git ls-remote refs/heads/master

When we believe this library is ready for use, we will begin publishing releases to Maven central.

Developer Information

Copyright and License

Copyright (c) Rich Hickey, and contributors, 2018-2020. All rights reserved. The use and distribution terms for this software are covered by the Eclipse Public License 1.0 ( which can be found in the file epl-v10.html at the root of this distribution. By using this software in any fashion, you are agreeing to be bound bythe terms of this license. You must not remove this notice, or any other, from this software.