diff --git a/err/defaults.go b/err/defaults.go
index 9ce8dc6..0bb40a9 100644
--- a/err/defaults.go
+++ b/err/defaults.go
@@ -1,34 +1,78 @@
 package err
 
 var (
-	/* Base */
+	// Success represents a generic successful controller execution
 	Success = Error{0, "all right", nil}
+
+	// Failure is the more generic error
 	Failure = Error{1, "it failed", nil}
+
+	// Unknown represents any error which cause is unknown.
+	// It might also be used for debug purposes as this error
+	// has to be used the less possible
 	Unknown = Error{-1, "", nil}
 
-	NoMatchFound  = Error{2, "no resource found", nil}
+	// NoMatchFound has to be set when trying to fetch data and there is no result
+	NoMatchFound = Error{2, "no resource found", nil}
+
+	// AlreadyExists has to be set when trying to insert data, but identifiers or
+	// unique fields already exists
 	AlreadyExists = Error{3, "resource already exists", nil}
 
+	// Config has to be set when there is a configuration error
 	Config = Error{4, "configuration error", nil}
 
-	/* I/O */
-	Upload                 = Error{100, "upload failed", nil}
-	Download               = Error{101, "download failed", nil}
+	// Upload has to be set when a file upload failed
+	Upload = Error{100, "upload failed", nil}
+
+	// Download has to be set when a file download failed
+	Download = Error{101, "download failed", nil}
+
+	// MissingDownloadHeaders has to be set when the implementation
+	// of a controller of type 'download' (which returns a file instead of
+	// a set or output fields) is missing its HEADER field
 	MissingDownloadHeaders = Error{102, "download headers are missing", nil}
-	MissingDownloadBody    = Error{103, "download body is missing", nil}
 
-	/* Controllers */
-	UnknownController    = Error{200, "unknown controller", nil}
-	UnknownMethod        = Error{201, "unknown method", nil}
+	// MissingDownloadBody has to be set when the implementation
+	// of a controller of type 'download' (which returns a file instead of
+	// a set or output fields) is missing its BODY field
+	MissingDownloadBody = Error{103, "download body is missing", nil}
+
+	// UnknownController is set when there is no controller matching
+	// the http request URI.
+	UnknownController = Error{200, "unknown controller", nil}
+
+	// UnknownMethod is set when there is no method matching the
+	// request's http method
+	UnknownMethod = Error{201, "unknown method", nil}
+
+	// UncallableController is set when there the requested controller's
+	// implementation (plugin file) is not found/callable
 	UncallableController = Error{202, "uncallable controller", nil}
-	UncallableMethod     = Error{203, "uncallable method", nil}
 
-	/* Permissions */
+	// UncallableMethod is set when there the requested controller's
+	// implementation does not features the requested method
+	UncallableMethod = Error{203, "uncallable method", nil}
+
+	// Permission is set when there is a permission error by default
+	// the api returns a permission error when the current scope (built
+	// by middlewares) does not match the scope required in the config.
+	// You can add your own permission policy and use this error
 	Permission = Error{300, "permission error", nil}
-	Token      = Error{301, "token error", nil}
 
-	/* Check */
-	MissingParam        = Error{400, "missing parameter", nil}
-	InvalidParam        = Error{401, "invalid parameter", nil}
+	// Token has to be set (usually in authentication middleware) to tell
+	// the user that this authentication token is expired or invalid
+	Token = Error{301, "token error", nil}
+
+	// MissingParam is set when a *required* parameter is missing from the
+	// http request
+	MissingParam = Error{400, "missing parameter", nil}
+
+	// InvalidParam is set when a given parameter fails its type check as
+	// defined in the config file.
+	InvalidParam = Error{401, "invalid parameter", nil}
+
+	// InvalidDefaultParam is set when an optional parameter's default value
+	// does not match its type.
 	InvalidDefaultParam = Error{402, "invalid default param", nil}
 )