diff --git a/docs/quickstart.rst b/docs/quickstart.rst
index 24bc284..4e5b5db 100644
--- a/docs/quickstart.rst
+++ b/docs/quickstart.rst
@@ -41,8 +41,7 @@ by reading YANG library data [RFC7895]_ from a file:
    'Data model ID: 9a9b7d2d28d4d78fa42e12348346990e3fb1c1b9'
 
 .. note::
-   Distribution directory *tools/python* contains the script *mkylib.py* that
-   can help with preparing YANG library data.
+   YANG library data can be created by running *yangson-mkylib*.
 
 Here is an ASCII art depicting the schema tree:
 
diff --git a/setup.py b/setup.py
index 57e1cac..cb21587 100644
--- a/setup.py
+++ b/setup.py
@@ -10,7 +10,8 @@
     author_email = "lhotka@nic.cz",
     url = "https://github.com/CZ-NIC/yangson",
     entry_points = {
-        "console_scripts": ["yangson=yangson.__main__:main"]
+        "console_scripts": ["yangson=yangson.__main__:main",
+                            "yangson-mkylib=yangson.mkylib:main"]
         },
     install_requires = ["PyXB"],
     tests_require = ["pytest"],
diff --git a/tools/python/mkylib.py b/yangson/mkylib.py
similarity index 87%
rename from tools/python/mkylib.py
rename to yangson/mkylib.py
index c748cc8..2d4014d 100644
--- a/tools/python/mkylib.py
+++ b/yangson/mkylib.py
@@ -14,7 +14,6 @@
 
 from yangson.statement import ModuleParser
 
-ydir = sys.argv[1]
 """Name of the directory with YANG (sub)modules."""
 data_kws = ["augment", "container", "leaf", "leaf-list", "list", "rpc", "notification", "identity"]
 """Keywords of statements that contribute nodes to the schema tree."""
@@ -23,6 +22,9 @@
 submodmap = {}
 """Dictionary for collecting submodule data."""
 
+class GeneratingError(Exception):
+    """Error when producing ietf-yang-library data"""
+
 
 def module_entry(yfile):
     """Add entry for one file containing YANG module text.
@@ -63,7 +65,7 @@ def module_entry(yfile):
         modmap[(mst.argument, rev)] = rec
 
 
-def main():
+def process_directory(ydir):
     for infile in os.listdir(ydir):
         if not infile.endswith(".yang"):
             continue
@@ -82,13 +84,11 @@ def main():
             try:
                 srec = submodmap[subm]
             except KeyError:
-                print(f"Submodule {subm} not available.", file=sys.stderr)
-                return 1
+                raise GeneratingError(f"Submodule {subm} not available.")
             if srev is None or srev == srec["revision"]:
                 sen["revision"] = srec["revision"]
             else:
-                print(f"Submodule {subm} revision mismatch.", file=sys.stderr)
-                return 1
+                raise GeneratingError(f"Submodule {subm} revision mismatch.")
             imp_only = imp_only or srec["import-only"]
             fts += srec["features"]
             sarr.append(sen)
@@ -104,9 +104,16 @@ def main():
             "module": marr
         }
     }
-    print(json.dumps(res, indent=2))
-    return 0
+    return res
+
+
+def main():
+    try:
+        print(json.dumps(process_directory(sys.argv[1]), indent=2))
+    except GeneratingError as e:
+        print(e, file=sys.stderr)
+        sys.exit(1)
 
 
 if __name__ == '__main__':
-    sys.exit(main())
+    main()