diff --git a/src/StaticPHP/Command/ReturnCode.php b/src/StaticPHP/Command/ReturnCode.php
index d152101e..5accebc3 100644
--- a/src/StaticPHP/Command/ReturnCode.php
+++ b/src/StaticPHP/Command/ReturnCode.php
@@ -17,26 +17,28 @@ trait ReturnCode
 {
     public const int OK = 0;
 
-    public const SUCCESS = 0; // alias of OK
+    public const SUCCESS = 0; // alias
 
-    public const int INTERNAL_ERROR = 1; // unsorted or internal error
+    public const FAILURE = 1; // generic failure
 
-    /** @deprecated Use specified error code instead */
-    public const FAILURE = 1;
+    // 64-69: reserved for standard errors
+    public const int USER_ERROR = 64; // wrong usage, bad arguments
 
-    public const int USER_ERROR = 2; // wrong usage or user error
+    public const int VALIDATION_ERROR = 65; // invalid input or config values
 
-    public const int ENVIRONMENT_ERROR = 3; // environment not suitable for operation
+    public const int ENVIRONMENT_ERROR = 69; // required tools/env not available
 
-    public const int VALIDATION_ERROR = 4; // validation failed
+    // 70+: application-specific errors
+    public const int INTERNAL_ERROR = 70; // internal logic error or unexpected state
 
-    public const int FILE_SYSTEM_ERROR = 5; // file system related error
+    public const int BUILD_ERROR = 72; // build / compile process failed
 
-    public const int DOWNLOAD_ERROR = 6; // network related error
+    public const int PATCH_ERROR = 73; // patching or modifying files failed
 
-    public const int BUILD_ERROR = 7; // build process error
+    public const int FILE_SYSTEM_ERROR = 74; // filesystem / IO error
 
-    public const int PATCH_ERROR = 8; // patching process error
+    public const int DOWNLOAD_ERROR = 75; // network / remote resource error
 
-    public const int INTERRUPT_SIGNAL = 130; // process interrupted by user (e.g., Ctrl+C)
+    // 128+: reserved for standard signals and interrupts
+    public const int INTERRUPT_SIGNAL = 130; // SIGINT (Ctrl+C)
 }