diff --git a/loader.py b/loader.py
index 51fd984..5b3e75b 100644
--- a/loader.py
+++ b/loader.py
@@ -9,6 +9,10 @@ def formatNumber(num):
     val.reverse()
     return str(int("0x" + "{0:0{1}x}".format(int(binascii.hexlify(val), 16), 64), 0))
 
+if len(sys.argv) != 5:
+    print("Correct loader's invocation should contain 4 parameters:\n1) Path to verifier key JSON\n2) Path to proof JSON\n3) Deployed contract address\n4) URL of RPC endpoint\n\nFor example:\npython loader.py verifier-key.json compressed-snark.json 0x720472c8ce72c2a2d711333e064abd3e6bbeadd3 http://127.0.0.1:8545")
+    os.exit(1)
+
 vk_file = sys.argv[1]
 if not os.path.exists(vk_file):
     print("verifier-key (json) input file is missing")