diff --git a/README.md b/README.md
index 2ff3a93..6464118 100644
--- a/README.md
+++ b/README.md
@@ -77,6 +77,38 @@ $ gitwerk semver major
 v1.0.0
 ```
 
+### sci
+
+gitwerk supports to run user-defined scripts written in clojure (powered by [borkdude/sci](https://github.com/borkdude/sci)).
+
+```
+## can read stdin
+$ echo '(semver ctx ["patch"])' | gitwerk sci
+v0.0.2
+
+## also read a file as a script
+$ cat examples/example1.clj
+(semver ctx ["patch"])
+$ gitwerk sci examples/example1.clj
+v0.0.3
+
+## fetch executed command result and modify returned message
+$ cat examples/example2.clj
+(let [res (semver-auto ctx nil)
+      status (get-in res [:console-out :status])
+      oldv (get-in res [:console-out :old-version])
+      newv (get-in res [:console-out :new-version])]
+  (if (= status :updated)
+    (str "Version updated: " oldv " -> " newv)
+    "Version not updated"))
+$ gitwerk sci examples/example2.clj
+Version not updated
+
+$ git commit --allow-empty -m "[patch] version updated"
+$ gitwerk sci examples/example2.clj
+Version updated: v0.0.3 -> v0.0.4
+```
+
 ## License
 
 Copyright © 2019 rinx
diff --git a/examples/example1.clj b/examples/example1.clj
new file mode 100644
index 0000000..9fa2323
--- /dev/null
+++ b/examples/example1.clj
@@ -0,0 +1 @@
+(semver ctx ["patch"])
diff --git a/examples/example2.clj b/examples/example2.clj
new file mode 100644
index 0000000..23a0152
--- /dev/null
+++ b/examples/example2.clj
@@ -0,0 +1,7 @@
+(let [res (semver-auto ctx nil)
+      status (get-in res [:console-out :status])
+      oldv (get-in res [:console-out :old-version])
+      newv (get-in res [:console-out :new-version])]
+  (if (= status :updated)
+    (str "Version updated: " oldv " -> " newv)
+    "Version not updated"))
diff --git a/project.clj b/project.clj
index c9a2891..2fe512f 100644
--- a/project.clj
+++ b/project.clj
@@ -9,6 +9,7 @@
                  [metosin/jsonista "0.2.2"]
                  [camel-snake-kebab "0.4.0"]
                  [io.quarkus/quarkus-jgit "1.1.0.CR1"]
+                 [borkdude/sci "0.0.12-alpha.7"]
                  [org.martinklepsch/clj-http-lite "0.4.3"]]
   :profiles {:dev {:dependencies [[org.clojure/tools.namespace "0.2.11"]
                                   [orchestra "2019.02.06-1"]]
diff --git a/src/gitwerk/command/sci.clj b/src/gitwerk/command/sci.clj
new file mode 100644
index 0000000..1252791
--- /dev/null
+++ b/src/gitwerk/command/sci.clj
@@ -0,0 +1,34 @@
+(ns gitwerk.command.sci
+  (:require
+   [clojure.spec.alpha :as spec]
+   [clojure.pprint :as pprint]
+   [sci.core :as sci]
+   [gitwerk.internal.io :as internal.io]))
+
+(def clj-primitives
+  {'println println
+   'pprint pprint/pprint})
+
+(defn run-fn [sci-opts]
+  (fn [ctx args]
+    (try
+      (let [file (first args)
+            body (if (nil? file)
+                   (internal.io/read-from-stdin)
+                   (internal.io/safe-read file))
+            ctx (dissoc ctx :command :summary)
+            opts (-> sci-opts
+                     (update
+                       :bindings
+                       #(-> %
+                            (merge clj-primitives)
+                            (merge {'ctx ctx}))))
+            res (sci/eval-string body opts)]
+        (if (and (map? res) (:status res))
+          res
+          {:status 0
+           :console-out res}))
+      (catch Exception e
+        {:status 1
+         :console-out
+         {:error (.getMessage e)}}))))
diff --git a/src/gitwerk/core.clj b/src/gitwerk/core.clj
index cd528de..61bf955 100644
--- a/src/gitwerk/core.clj
+++ b/src/gitwerk/core.clj
@@ -3,6 +3,7 @@
    [clojure.spec.alpha :as spec]
    [clojure.tools.cli :as cli]
    [clojure.string :as string]
+   [clojure.pprint :as pprint]
    [clojure.edn :as edn]
    [clojure.java.io :as io]
    [gitwerk.service.runner :as runner])
@@ -10,19 +11,19 @@
 
 (def cli-header
   (string/join
-    "\n"
+   "\n"
+   (concat
     ["gitwerk is a CLI tool for supporting Git(Hub) operations on CI."
      ""
      "Usage: gitwerk [command] [options]"
      ""
-     "Available commands:"
-     "  clone [url]   clone git repository"
-     "  log           show git logs of current directory"
-     "  semver [type] print incremented version"
-     "  semver-auto   increment version by latest git log message contexts"
-     "  tag           show git tags of current directory"
-     ""
-     "Options:"]))
+     "Available commands:"]
+    (mapv (fn [[k v]]
+            (let [name (format "  %-12s " (name k))
+                  desc (:description v)]
+              (str name desc))) runner/definitions)
+    [""
+     "Options:"])))
 (def cli-options
   [["-f" "--file PATH" "config"
     :id :config-filename
@@ -33,19 +34,21 @@
 
 (defn edn-output
   [ctx res]
-  (println res))
+  (pprint/pprint res))
 
 (defn std-output
   [{:keys [summary] :as ctx}
    {:keys [status invalid-arg? console-out]}]
-    (when console-out
-      (println console-out))
-    (when invalid-arg?
-      (println cli-header)
-      (println summary))
-    (if status
-      (System/exit status)
-      (System/exit 1)))
+  (when console-out
+    (if (map? console-out)
+      (pprint/pprint console-out)
+      (println console-out)))
+  (when invalid-arg?
+    (println cli-header)
+    (println summary))
+  (if status
+    (System/exit status)
+    (System/exit 1)))
 
 (defn run
   [{:keys [options] :as ctx}]
diff --git a/src/gitwerk/internal/io.clj b/src/gitwerk/internal/io.clj
new file mode 100644
index 0000000..c511c83
--- /dev/null
+++ b/src/gitwerk/internal/io.clj
@@ -0,0 +1,20 @@
+(ns gitwerk.internal.io
+  (:require
+    [clojure.spec.alpha :as spec]
+    [clojure.java.io :as io]
+    [clojure.string :as string])
+  (:import
+    [java.io BufferedReader]))
+
+(defn read-from-stdin []
+  (->> (BufferedReader. *in*)
+       (line-seq)
+       (string/join "\n")))
+
+(defn safe-read
+  [file]
+  (if (.exists (io/file file))
+    (slurp file)
+    (throw
+      (Exception.
+        (str "File not found: " file)))))
diff --git a/src/gitwerk/service/runner.clj b/src/gitwerk/service/runner.clj
index 46b2519..6f53e78 100644
--- a/src/gitwerk/service/runner.clj
+++ b/src/gitwerk/service/runner.clj
@@ -4,22 +4,47 @@
    [camel-snake-kebab.core :as csk]
    [gitwerk.command.clone :as command.clone]
    [gitwerk.command.log :as command.log]
+   [gitwerk.command.sci :as command.sci]
    [gitwerk.command.semver :as command.semver]
    [gitwerk.command.semver-auto :as command.semver-auto]
    [gitwerk.command.tag :as command.tag]))
 
+(def primitives
+  {:clone
+   {:command command.clone/run
+    :description "clone git repository"}
+   :log
+   {:command command.log/run
+    :description "show git logs of current directory"}
+   :semver
+   {:command command.semver/run
+    :description "print incremented version"}
+   :semver-auto
+   {:command command.semver-auto/run
+    :description "increment version by latest git log message contexts"}
+   :tag
+   {:command command.tag/run
+    :description "show git tags of current directory"}})
+
+(def definitions
+  (let [->binding (fn [[k v]]
+                    (let [sym (symbol (name k))
+                          com (:command v)]
+                      [sym com]))
+        bindings (->> primitives
+                      (map ->binding)
+                      (into {}))
+        sci-opts {:bindings bindings}]
+    (into primitives
+          {:sci {:command (command.sci/run-fn sci-opts)
+                 :description "run user-defined script (written in clojure)"}})))
+
 (defn dispatch
   [{:keys [args] :as ctx} cmd]
   (let [default (fn [_ _]
                   {:status 1
                    :invalid-arg? true})
-        cmd (case cmd
-              :clone command.clone/run
-              :log command.log/run
-              :semver command.semver/run
-              :semver-auto command.semver-auto/run
-              :tag command.tag/run
-              default)]
+        cmd (or (:command (cmd definitions)) default)]
     (cmd ctx args)))
 
 (defn run