diff --git a/simple-ca.py b/simple-ca.py
old mode 100644
new mode 100755
index 2cc2fa1..c6efa64
--- a/simple-ca.py
+++ b/simple-ca.py
@@ -1,3 +1,4 @@
+#!/usr/bin/env python3
 # MIT License
 #
 # Copyright (c) 2026 Sławomir Koszewski
@@ -367,25 +368,25 @@ def _build_parser():
     sub = parser.add_subparsers(dest="command", required=True)
 
     p_ca = sub.add_parser("make-ca", help="Create a root or issuing CA.")
-    p_ca.add_argument("--days", type=int, default=3650)
-    p_ca.add_argument("--issuing-ca")
-    p_ca.add_argument("--aia-base-url")
-    p_ca.add_argument("ca_dir")
-    p_ca.add_argument("ca_name")
+    p_ca.add_argument("--days", type=int, default=3650, help="Validity period in days (default: 3650)")
+    p_ca.add_argument("--issuing-ca", help="Specify the issuing CA")
+    p_ca.add_argument("--aia-base-url", help="Specify the AIA base URL")
+    p_ca.add_argument("--ca-dir", help="Directory to store the CA files")
+    p_ca.add_argument("ca_name", help="Name of the CA")
 
     p_cert = sub.add_parser("make-cert", help="Create a server/client certificate.")
-    p_cert.add_argument("--ca-dir")
-    p_cert.add_argument("--issuing-ca")
-    p_cert.add_argument("--days", type=int, default=365)
-    p_cert.add_argument("cert_dir")
-    p_cert.add_argument("subject_name")
-    p_cert.add_argument("sans", nargs="*")
+    p_cert.add_argument("--ca-dir", help="Directory of the CA")
+    p_cert.add_argument("--issuing-ca", help="Specify the issuing CA")
+    p_cert.add_argument("--days", type=int, default=365, help="Validity period in days (default: 365)")
+    p_cert.add_argument("--cert-dir", help="Directory to store the certificate files")
+    p_cert.add_argument("subject_name", help="Subject name for the certificate")
+    p_cert.add_argument("sans", nargs="*", help="Subject Alternative Names (SANs) for the certificate")
 
     p_pfx = sub.add_parser("make-pfx", help="Create a PKCS#12 (PFX) bundle.")
-    p_pfx.add_argument("--ca-dir", required=True)
-    p_pfx.add_argument("--issuing-ca")
-    p_pfx.add_argument("--path", required=True, dest="cert_path")
-    p_pfx.add_argument("--password")
+    p_pfx.add_argument("--issuing-ca", help="Specify the issuing CA")
+    p_pfx.add_argument("--ca-dir", help="Directory of the CA")
+    p_pfx.add_argument("--password", help="Password for the PFX file")
+    p_pfx.add_argument("path", help="Path to the certificate file")
 
     return parser
 
@@ -393,10 +394,11 @@ def _build_parser():
 def main(argv=None):
     parser = _build_parser()
     args = parser.parse_args(argv)
+    ca_dir = args.ca_dir or os.environ.get("SIMPLE_CA_DIR") or os.getcwd()
 
     if args.command == "make-ca":
         ok = make_ca(
-            args.ca_dir, args.ca_name,
+            ca_dir, args.ca_name,
             days=args.days,
             issuing_ca=args.issuing_ca,
             aia_base_url=args.aia_base_url,
@@ -405,13 +407,13 @@ def main(argv=None):
         ok = make_cert(
             args.cert_dir, args.subject_name,
             sans=args.sans,
-            ca_dir=args.ca_dir,
+            ca_dir=ca_dir,
             issuing_ca=args.issuing_ca,
             days=args.days,
         )
     elif args.command == "make-pfx":
         ok = make_pfx(
-            args.cert_path, args.ca_dir,
+            args.path, ca_dir,
             issuing_ca=args.issuing_ca,
             password=args.password,
         )