diff --git a/silkaj/cli_tools.py b/silkaj/cli_tools.py
index 5aa0c6c8bf7530f9c98ce004426e94534453e928..1e658ecb1a7ac0625871a9e7ad49a363cc612433 100644
--- a/silkaj/cli_tools.py
+++ b/silkaj/cli_tools.py
@@ -22,17 +22,16 @@ class MutuallyExclusiveOption(Option):
         help = kwargs.get("help", "")
         if self.mutually_exclusive:
             ex_str = ", ".join(self.mutually_exclusive)
-            kwargs["help"] = help + (
-                " NOTE: This argument is mutually exclusive with "
-                " arguments: [" + ex_str + "]."
-            )
+            kwargs[
+                "help"
+            ] = f"{help} NOTE: This argument is mutually exclusive with arguments: [{ex_str}]."
         super().__init__(*args, **kwargs)
 
     def handle_parse_result(self, ctx, opts, args):
         if self.mutually_exclusive.intersection(opts) and self.name in opts:
+            arguments = ", ".join(self.mutually_exclusive)
             raise UsageError(
-                "Usage: `{}` is mutually exclusive with "
-                "arguments `{}`.".format(self.name, ", ".join(self.mutually_exclusive))
+                f"Usage: `{self.name}` is mutually exclusive with arguments `{arguments}`."
             )
 
         return super().handle_parse_result(ctx, opts, args)
diff --git a/silkaj/crypto_tools.py b/silkaj/crypto_tools.py
index 60ae6e54ac3c77584828c011373f498bba535055..429ffc657fcfef4192b8619342b1df216a132e6a 100644
--- a/silkaj/crypto_tools.py
+++ b/silkaj/crypto_tools.py
@@ -51,7 +51,7 @@ def check_pubkey_format(pubkey, display_error=True):
     elif re.search(re.compile(PUBKEY_CHECKSUM_PATTERN), pubkey):
         return True
     elif display_error:
-        message_exit("Error: bad format for following public key: " + pubkey)
+        message_exit(f"Error: bad format for following public key: {pubkey}")
     return
 
 
@@ -65,11 +65,8 @@ def validate_checksum(pubkey_checksum):
     if checksum == gen_checksum(pubkey):
         return pubkey
     message_exit(
-        "Error: public key '"
-        + pubkey
-        + "' does not match checksum '"
-        + checksum
-        + "'.\nPlease verify the public key."
+        f"Error: public key '{pubkey}' does not match checksum '{checksum}'.\n\
+Please verify the public key."
     )