diff --git a/internal/config/errors.go b/internal/config/errors.go
index 7ed4597..2a2df17 100644
--- a/internal/config/errors.go
+++ b/internal/config/errors.go
@@ -41,6 +41,9 @@ const ErrMissingDescription = cerr("missing description")
 // ErrIllegalOptionalURIParam - an URI parameter cannot be optional
 const ErrIllegalOptionalURIParam = cerr("URI parameter cannot be optional")
 
+// ErrOptionalOption - an output is optional
+const ErrOptionalOption = cerr("output cannot be optional")
+
 // ErrMissingParamDesc - a parameter is missing its description
 const ErrMissingParamDesc = cerr("missing parameter description")
 
diff --git a/internal/config/parameter.go b/internal/config/parameter.go
index 757a09e..1f8be92 100644
--- a/internal/config/parameter.go
+++ b/internal/config/parameter.go
@@ -1,6 +1,8 @@
 package config
 
-import "git.xdrm.io/go/aicra/datatype"
+import (
+	"git.xdrm.io/go/aicra/datatype"
+)
 
 // Validate implements the validator interface
 func (param *Parameter) Validate(datatypes ...datatype.T) error {
@@ -21,16 +23,14 @@ func (param *Parameter) Validate(datatypes ...datatype.T) error {
 	}
 
 	// assign the datatype
-	datatypeFound := false
 	for _, dtype := range datatypes {
 		param.Validator = dtype.Build(param.Type, datatypes...)
+		param.ExtractType = dtype.Type()
 		if param.Validator != nil {
-			datatypeFound = true
-			param.ExtractType = dtype.Type()
 			break
 		}
 	}
-	if !datatypeFound {
+	if param.Validator == nil {
 		return ErrUnknownDataType
 	}
 
diff --git a/internal/config/service.go b/internal/config/service.go
index 0fc3164..87815d7 100644
--- a/internal/config/service.go
+++ b/internal/config/service.go
@@ -108,6 +108,12 @@ func (svc *Service) Validate(datatypes ...datatype.T) error {
 		}
 	}
 
+	// check output
+	err = svc.validateOutput(datatypes)
+	if err != nil {
+		return fmt.Errorf("field 'out': %w", err)
+	}
+
 	return nil
 }
 
@@ -257,3 +263,52 @@ func (svc *Service) validateInput(types []datatype.T) error {
 
 	return nil
 }
+
+func (svc *Service) validateOutput(types []datatype.T) error {
+
+	// ignore no parameter
+	if svc.Output == nil || len(svc.Output) < 1 {
+		svc.Output = make(map[string]*Parameter, 0)
+		return nil
+	}
+
+	// for each parameter
+	for paramName, param := range svc.Output {
+		if len(paramName) < 1 {
+			return fmt.Errorf("%s: %w", paramName, ErrIllegalParamName)
+		}
+
+		// use param name if no rename
+		if len(param.Rename) < 1 {
+			param.Rename = paramName
+		}
+
+		err := param.Validate(types...)
+		if err != nil {
+			return fmt.Errorf("%s: %w", paramName, err)
+		}
+
+		if param.Optional {
+			return fmt.Errorf("%s: %w", paramName, ErrOptionalOption)
+		}
+
+		// fail on name/rename conflict
+		for paramName2, param2 := range svc.Output {
+			// ignore self
+			if paramName == paramName2 {
+				continue
+			}
+
+			// 3.2.1. Same rename field
+			// 3.2.2. Not-renamed field matches a renamed field
+			// 3.2.3. Renamed field matches name
+			if param.Rename == param2.Rename || paramName == param2.Rename || paramName2 == param.Rename {
+				return fmt.Errorf("%s: %w", paramName, ErrParamNameConflict)
+			}
+
+		}
+
+	}
+
+	return nil
+}