diff --git a/internal/index/index.go b/internal/index/index.go
index 3b93b5f..1a630b2 100644
--- a/internal/index/index.go
+++ b/internal/index/index.go
@@ -8,13 +8,18 @@ import (
 	"github.com/marte-community/marte-dev-tools/internal/parser"
 )
 
+type VariableInfo struct {
+	Def  *parser.VariableDefinition
+	File string
+}
+
 type ProjectTree struct {
 	Root          *ProjectNode
 	References    []Reference
 	IsolatedFiles map[string]*ProjectNode
 	GlobalPragmas map[string][]string
 	NodeMap       map[string][]*ProjectNode
-	Variables     map[string]*parser.VariableDefinition
+	Variables     map[string]VariableInfo
 }
 
 func (pt *ProjectTree) ScanDirectory(rootPath string) error {
@@ -74,7 +79,7 @@ func NewProjectTree() *ProjectTree {
 		},
 		IsolatedFiles: make(map[string]*ProjectNode),
 		GlobalPragmas: make(map[string][]string),
-		Variables:     make(map[string]*parser.VariableDefinition),
+		Variables:     make(map[string]VariableInfo),
 	}
 }
 
@@ -224,7 +229,7 @@ func (pt *ProjectTree) populateNode(node *ProjectNode, file string, config *pars
 			pt.indexValue(file, d.Value)
 		case *parser.VariableDefinition:
 			fileFragment.Definitions = append(fileFragment.Definitions, d)
-			pt.Variables[d.Name] = d
+			pt.Variables[d.Name] = VariableInfo{Def: d, File: file}
 		case *parser.ObjectNode:
 			fileFragment.Definitions = append(fileFragment.Definitions, d)
 			norm := NormalizeName(d.Name)
@@ -282,7 +287,7 @@ func (pt *ProjectTree) addObjectFragment(node *ProjectNode, file string, obj *pa
 			pt.extractFieldMetadata(node, d)
 		case *parser.VariableDefinition:
 			frag.Definitions = append(frag.Definitions, d)
-			pt.Variables[d.Name] = d
+			pt.Variables[d.Name] = VariableInfo{Def: d, File: file}
 		case *parser.ObjectNode:
 			frag.Definitions = append(frag.Definitions, d)
 			norm := NormalizeName(d.Name)
@@ -418,7 +423,7 @@ func (pt *ProjectTree) ResolveReferences() {
 		ref := &pt.References[i]
 
 		if v, ok := pt.Variables[ref.Name]; ok {
-			ref.TargetVariable = v
+			ref.TargetVariable = v.Def
 			continue
 		}
 
diff --git a/internal/schema/marte.cue b/internal/schema/marte.cue
index 6ad8caa..5cb8de6 100644
--- a/internal/schema/marte.cue
+++ b/internal/schema/marte.cue
@@ -413,7 +413,7 @@ package schema
 	OPCUA: {...}
 	SysLogger: {...}
 	GAMDataSource: {
-		#meta: multithreaded: bool | *false
+		#meta: multithreaded: false
 		#meta: direction:     "INOUT"
 		#meta: type:          "datasource"
 		...
@@ -421,7 +421,7 @@ package schema
 }
 
 #Meta: {
-	direction?: "IN" | "OUT" | "INOUT"
+	direction?:     "IN" | "OUT" | "INOUT"
 	multithreaded?: bool
 	...
 }
@@ -430,7 +430,7 @@ package schema
 // It must have a Class field.
 // Based on Class, it validates against #Classes.
 #Object: {
-	Class: string
+	Class:    string
 	"#meta"?: #Meta
 	// Allow any other field by default (extensibility),
 	// unless #Classes definition is closed.
diff --git a/internal/validator/validator.go b/internal/validator/validator.go
index 2d20b80..f29ed3a 100644
--- a/internal/validator/validator.go
+++ b/internal/validator/validator.go
@@ -56,6 +56,7 @@ func (v *Validator) ValidateProject() {
 	v.CheckUnused()
 	v.CheckDataSourceThreading()
 	v.CheckINOUTOrdering()
+	v.CheckVariables()
 }
 
 func (v *Validator) validateNode(node *index.ProjectNode) {
@@ -936,53 +937,111 @@ func (v *Validator) CheckINOUTOrdering() {
 		}
 
 		for _, thread := range threads {
-			producedSignals := make(map[*index.ProjectNode]bool)
+			producedSignals := make(map[*index.ProjectNode]map[string][]*index.ProjectNode)
+			consumedSignals := make(map[*index.ProjectNode]map[string]bool)
+
 			gams := v.getThreadGAMs(thread)
 			for _, gam := range gams {
-				v.processGAMSignalsForOrdering(gam, "InputSignals", producedSignals, true, thread, state)
-				v.processGAMSignalsForOrdering(gam, "OutputSignals", producedSignals, false, thread, state)
+				v.processGAMSignalsForOrdering(gam, "InputSignals", producedSignals, consumedSignals, true, thread, state)
+				v.processGAMSignalsForOrdering(gam, "OutputSignals", producedSignals, consumedSignals, false, thread, state)
+			}
+
+			// Check for produced but not consumed
+			for ds, signals := range producedSignals {
+				for sigName, producers := range signals {
+					consumed := false
+					if cSet, ok := consumedSignals[ds]; ok {
+						if cSet[sigName] {
+							consumed = true
+						}
+					}
+					if !consumed {
+						for _, prod := range producers {
+							v.Diagnostics = append(v.Diagnostics, Diagnostic{
+								Level:    LevelWarning,
+								Message:  fmt.Sprintf("INOUT Signal '%s' (DS '%s') is produced in thread '%s' but never consumed in the same thread.", sigName, ds.RealName, thread.RealName),
+								Position: v.getNodePosition(prod),
+								File:     v.getNodeFile(prod),
+							})
+						}
+					}
+				}
 			}
 		}
 	}
 }
 
-func (v *Validator) processGAMSignalsForOrdering(gam *index.ProjectNode, containerName string, produced map[*index.ProjectNode]bool, isInput bool, thread, state *index.ProjectNode) {
+func (v *Validator) processGAMSignalsForOrdering(gam *index.ProjectNode, containerName string, produced map[*index.ProjectNode]map[string][]*index.ProjectNode, consumed map[*index.ProjectNode]map[string]bool, isInput bool, thread, state *index.ProjectNode) {
 	container := gam.Children[containerName]
 	if container == nil {
 		return
 	}
 
 	for _, sig := range container.Children {
-		if sig.Target == nil {
+		fields := v.getFields(sig)
+		var dsNode *index.ProjectNode
+		var sigName string
+
+		if sig.Target != nil {
+			if sig.Target.Parent != nil && sig.Target.Parent.Parent != nil {
+				dsNode = sig.Target.Parent.Parent
+				sigName = sig.Target.RealName
+			}
+		}
+
+		if dsNode == nil {
+			if dsFields, ok := fields["DataSource"]; ok && len(dsFields) > 0 {
+				dsName := v.getFieldValue(dsFields[0])
+				dsNode = v.resolveReference(dsName, v.getNodeFile(sig), isDataSource)
+			}
+			if aliasFields, ok := fields["Alias"]; ok && len(aliasFields) > 0 {
+				sigName = v.getFieldValue(aliasFields[0])
+			} else {
+				sigName = sig.RealName
+			}
+		}
+
+		if dsNode == nil || sigName == "" {
 			continue
 		}
 
-		targetSig := sig.Target
-		if targetSig.Parent == nil || targetSig.Parent.Parent == nil {
-			continue
-		}
-		ds := targetSig.Parent.Parent
+		sigName = index.NormalizeName(sigName)
 
-		if v.isMultithreaded(ds) {
+		if v.isMultithreaded(dsNode) {
 			continue
 		}
 
-		dir := v.getDataSourceDirection(ds)
+		dir := v.getDataSourceDirection(dsNode)
 		if dir != "INOUT" {
 			continue
 		}
 
 		if isInput {
-			if !produced[targetSig] {
+			isProduced := false
+			if set, ok := produced[dsNode]; ok {
+				if len(set[sigName]) > 0 {
+					isProduced = true
+				}
+			}
+
+			if !isProduced {
 				v.Diagnostics = append(v.Diagnostics, Diagnostic{
 					Level:    LevelError,
-					Message:  fmt.Sprintf("INOUT Signal '%s' (DS '%s') is consumed by GAM '%s' in thread '%s' (State '%s') before being produced by any previous GAM.", targetSig.RealName, ds.RealName, gam.RealName, thread.RealName, state.RealName),
+					Message:  fmt.Sprintf("INOUT Signal '%s' (DS '%s') is consumed by GAM '%s' in thread '%s' (State '%s') before being produced by any previous GAM.", sigName, dsNode.RealName, gam.RealName, thread.RealName, state.RealName),
 					Position: v.getNodePosition(sig),
 					File:     v.getNodeFile(sig),
 				})
 			}
+
+			if consumed[dsNode] == nil {
+				consumed[dsNode] = make(map[string]bool)
+			}
+			consumed[dsNode][sigName] = true
 		} else {
-			produced[targetSig] = true
+			if produced[dsNode] == nil {
+				produced[dsNode] = make(map[string][]*index.ProjectNode)
+			}
+			produced[dsNode][sigName] = append(produced[dsNode][sigName], sig)
 		}
 	}
 }
@@ -1003,3 +1062,42 @@ func (v *Validator) getDataSourceDirection(ds *index.ProjectNode) string {
 	}
 	return ""
 }
+
+func (v *Validator) CheckVariables() {
+	if v.Schema == nil {
+		return
+	}
+	ctx := v.Schema.Context
+
+	for _, info := range v.Tree.Variables {
+		def := info.Def
+
+		// Compile Type
+		typeVal := ctx.CompileString(def.TypeExpr)
+		if typeVal.Err() != nil {
+			v.Diagnostics = append(v.Diagnostics, Diagnostic{
+				Level:    LevelError,
+				Message:  fmt.Sprintf("Invalid type expression for variable '%s': %v", def.Name, typeVal.Err()),
+				Position: def.Position,
+				File:     info.File,
+			})
+			continue
+		}
+
+		if def.DefaultValue != nil {
+			valInterface := v.valueToInterface(def.DefaultValue)
+			valVal := ctx.Encode(valInterface)
+
+			// Unify
+			res := typeVal.Unify(valVal)
+			if err := res.Validate(cue.Concrete(true)); err != nil {
+				v.Diagnostics = append(v.Diagnostics, Diagnostic{
+					Level:    LevelError,
+					Message:  fmt.Sprintf("Variable '%s' value mismatch: %v", def.Name, err),
+					Position: def.Position,
+					File:     info.File,
+				})
+			}
+		}
+	}
+}
diff --git a/test/formatter_variables_test.go b/test/formatter_variables_test.go
new file mode 100644
index 0000000..76d7d5d
--- /dev/null
+++ b/test/formatter_variables_test.go
@@ -0,0 +1,45 @@
+package integration
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"github.com/marte-community/marte-dev-tools/internal/formatter"
+	"github.com/marte-community/marte-dev-tools/internal/parser"
+)
+
+func TestFormatterVariables(t *testing.T) {
+	content := `
+#var MyInt: int = 10
+#var MyStr: string | "A" = "default"
+
++Obj = {
+    Field1 = $MyInt
+    Field2 = $MyStr
+}
+`
+	p := parser.NewParser(content)
+	cfg, err := p.Parse()
+	if err != nil {
+		t.Fatalf("Parse failed: %v", err)
+	}
+
+	var buf bytes.Buffer
+	formatter.Format(cfg, &buf)
+
+	output := buf.String()
+
+	// Parser reconstructs type expression with spaces
+	if !strings.Contains(output, "#var MyInt: int = 10") {
+		t.Errorf("Variable MyInt formatted incorrectly. Got:\n%s", output)
+	}
+	// Note: parser adds space after each token in TypeExpr
+	// string | "A" -> "string | \"A\"" 
+	if !strings.Contains(output, "#var MyStr: string | \"A\" = \"default\"") {
+		t.Errorf("Variable MyStr formatted incorrectly. Got:\n%s", output)
+	}
+	if !strings.Contains(output, "Field1 = $MyInt") {
+		t.Errorf("Variable reference $MyInt formatted incorrectly. Got:\n%s", output)
+	}
+}
diff --git a/test/lsp_inout_test.go b/test/lsp_inout_test.go
new file mode 100644
index 0000000..90f489c
--- /dev/null
+++ b/test/lsp_inout_test.go
@@ -0,0 +1,73 @@
+package integration
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"github.com/marte-community/marte-dev-tools/internal/index"
+	"github.com/marte-community/marte-dev-tools/internal/lsp"
+	"github.com/marte-community/marte-dev-tools/internal/schema"
+)
+
+func TestLSPINOUTOrdering(t *testing.T) {
+	lsp.Tree = index.NewProjectTree()
+	lsp.Documents = make(map[string]string)
+	// Mock schema if necessary, but we rely on internal schema
+	lsp.GlobalSchema = schema.LoadFullSchema(".")
+
+	var buf bytes.Buffer
+	lsp.Output = &buf
+
+	content := `
++App = {
+  Class = RealTimeApplication
+  +Data = {
+    Class = ReferenceContainer
+    +DDB = {
+      Class = GAMDataSource
+    }
+  }
+  +Functions = {
+    Class = ReferenceContainer
+    +A = {
+      Class = IOGAM
+      InputSignals = {
+        A = {
+          DataSource = DDB
+          Type = uint32
+        }
+      }
+      OutputSignals = {
+        B = {
+          DataSource = DDB
+          Type = uint32
+        }
+      }
+    }
+  }
+  +States = {
+    Class = ReferenceContainer
+    +State = {
+      Class =RealTimeState
+      Threads = {
+        +Th1 = {
+          Class = RealTimeThread
+          Functions = {A}
+        }
+      }
+    }
+  }
+}
+`
+	uri := "file://app.marte"
+	lsp.HandleDidOpen(lsp.DidOpenTextDocumentParams{
+		TextDocument: lsp.TextDocumentItem{URI: uri, Text: content},
+	})
+
+	output := buf.String()
+	if !strings.Contains(output, "INOUT Signal 'A'") {
+		t.Error("LSP did not report INOUT ordering error")
+		t.Log(output)
+	}
+}
diff --git a/test/lsp_inout_warning_test.go b/test/lsp_inout_warning_test.go
new file mode 100644
index 0000000..1a01418
--- /dev/null
+++ b/test/lsp_inout_warning_test.go
@@ -0,0 +1,66 @@
+package integration
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"github.com/marte-community/marte-dev-tools/internal/index"
+	"github.com/marte-community/marte-dev-tools/internal/lsp"
+	"github.com/marte-community/marte-dev-tools/internal/schema"
+)
+
+func TestLSPINOUTWarning(t *testing.T) {
+	lsp.Tree = index.NewProjectTree()
+	lsp.Documents = make(map[string]string)
+	lsp.GlobalSchema = schema.LoadFullSchema(".")
+
+	var buf bytes.Buffer
+	lsp.Output = &buf
+
+	content := `
++App = {
+  Class = RealTimeApplication
+  +Data = {
+    Class = ReferenceContainer
+    +DDB = {
+      Class = GAMDataSource
+    }
+  }
+  +Functions = {
+    Class = ReferenceContainer
+    +Producer = {
+      Class = IOGAM
+      OutputSignals = {
+        ProducedSig = {
+          DataSource = DDB
+          Type = uint32
+        }
+      }
+    }
+  }
+  +States = {
+    Class = ReferenceContainer
+    +State = {
+      Class =RealTimeState
+      Threads = {
+        +Th1 = {
+          Class = RealTimeThread
+          Functions = {Producer}
+        }
+      }
+    }
+  }
+}
+`
+	uri := "file://warning.marte"
+	lsp.HandleDidOpen(lsp.DidOpenTextDocumentParams{
+		TextDocument: lsp.TextDocumentItem{URI: uri, Text: content},
+	})
+
+	output := buf.String()
+	if !strings.Contains(output, "produced in thread '+Th1' but never consumed") {
+		t.Error("LSP did not report INOUT usage warning")
+		t.Log(output)
+	}
+}
diff --git a/test/validator_inout_ordering_test.go b/test/validator_inout_ordering_test.go
new file mode 100644
index 0000000..c7ed2c4
--- /dev/null
+++ b/test/validator_inout_ordering_test.go
@@ -0,0 +1,93 @@
+package integration
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/marte-community/marte-dev-tools/internal/index"
+	"github.com/marte-community/marte-dev-tools/internal/parser"
+	"github.com/marte-community/marte-dev-tools/internal/validator"
+)
+
+func TestINOUTOrdering(t *testing.T) {
+	content := `
++Data = {
+    Class = ReferenceContainer
+    +MyDS = {
+        Class = GAMDataSource
+        #meta = { multithreaded = false } // Explicitly false
+        Signals = { Sig1 = { Type = uint32 } }
+    }
+}
++GAM_Consumer = {
+    Class = IOGAM
+    InputSignals = {
+        Sig1 = { DataSource = MyDS Type = uint32 }
+    }
+}
++GAM_Producer = {
+    Class = IOGAM
+    OutputSignals = {
+        Sig1 = { DataSource = MyDS Type = uint32 }
+    }
+}
++App = {
+    Class = RealTimeApplication
+    +States = {
+        Class = ReferenceContainer
+        +State1 = {
+            Class = RealTimeState
+            +Thread1 = {
+                Class = RealTimeThread
+                Functions = { GAM_Consumer, GAM_Producer } // Fail
+            }
+        }
+        +State2 = {
+            Class = RealTimeState
+            +Thread2 = {
+                Class = RealTimeThread
+                Functions = { GAM_Producer, GAM_Consumer } // Pass
+            }
+        }
+    }
+}
+`
+	pt := index.NewProjectTree()
+	p := parser.NewParser(content)
+	cfg, err := p.Parse()
+	if err != nil {
+		t.Fatal(err)
+	}
+	pt.AddFile("main.marte", cfg)
+
+	// Use validator with default schema (embedded)
+	// We pass "." but it shouldn't matter if no .marte_schema.cue exists
+	v := validator.NewValidator(pt, ".")
+	v.ValidateProject()
+
+	foundError := false
+	for _, d := range v.Diagnostics {
+		if strings.Contains(d.Message, "consumed by GAM '+GAM_Consumer'") &&
+			strings.Contains(d.Message, "before being produced") {
+			foundError = true
+		}
+	}
+
+	if !foundError {
+		t.Error("Expected INOUT ordering error for State1")
+		for _, d := range v.Diagnostics {
+			t.Logf("Diag: %s", d.Message)
+		}
+	}
+
+	foundErrorState2 := false
+	for _, d := range v.Diagnostics {
+		if strings.Contains(d.Message, "State '+State2'") && strings.Contains(d.Message, "before being produced") {
+			foundErrorState2 = true
+		}
+	}
+
+	if foundErrorState2 {
+		t.Error("Unexpected INOUT ordering error for State2 (Correct order)")
+	}
+}
diff --git a/test/variables_test.go b/test/variables_test.go
new file mode 100644
index 0000000..2b0637c
--- /dev/null
+++ b/test/variables_test.go
@@ -0,0 +1,72 @@
+package integration
+
+import (
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/marte-community/marte-dev-tools/internal/builder"
+	"github.com/marte-community/marte-dev-tools/internal/parser"
+)
+
+func TestVariables(t *testing.T) {
+	content := `
+#var MyInt: int = 10
+#var MyStr: string = "default"
+
++Obj = {
+    Class = Test
+    Field1 = $MyInt
+    Field2 = $MyStr
+}
+`
+	// Test Parsing
+	p := parser.NewParser(content)
+	cfg, err := p.Parse()
+	if err != nil {
+		t.Fatalf("Parse failed: %v", err)
+	}
+
+	// Check definitions: #var, #var, +Obj
+	if len(cfg.Definitions) != 3 {
+		t.Errorf("Expected 3 definitions, got %d", len(cfg.Definitions))
+	}
+
+	// Test Builder resolution
+	f, _ := os.CreateTemp("", "vars.marte")
+	f.WriteString(content)
+	f.Close()
+	defer os.Remove(f.Name())
+
+	// Build with override
+	overrides := map[string]string{
+		"MyInt": "999",
+	}
+
+	b := builder.NewBuilder([]string{f.Name()}, overrides)
+
+	outF, _ := os.CreateTemp("", "out.marte")
+	outName := outF.Name()
+	defer os.Remove(outName)
+
+	err = b.Build(outF)
+	outF.Close()
+
+	if err != nil {
+		t.Fatalf("Build failed: %v", err)
+	}
+
+	outContent, _ := os.ReadFile(outName)
+	outStr := string(outContent)
+
+	if !strings.Contains(outStr, "Field1 = 999") {
+		t.Errorf("Variable override failed for MyInt. Got:\n%s", outStr)
+	}
+	if !strings.Contains(outStr, "Field2 = \"default\"") {
+		t.Errorf("Default value failed for MyStr. Got:\n%s", outStr)
+	}
+	// Check #var is removed
+	if strings.Contains(outStr, "#var") {
+		t.Error("#var definition present in output")
+	}
+}