diff --git a/internal/index/index.go b/internal/index/index.go
index 7563763..6c8cb89 100644
--- a/internal/index/index.go
+++ b/internal/index/index.go
@@ -7,7 +7,15 @@ import (
 )
 
 type ProjectTree struct {
-	Root *ProjectNode
+	Root       *ProjectNode
+	References []Reference
+}
+
+type Reference struct {
+	Name     string
+	Position parser.Position
+	File     string
+	Target   *ProjectNode // Resolved target
 }
 
 type ProjectNode struct {
@@ -15,13 +23,14 @@ type ProjectNode struct {
 	RealName  string // The actual name used in definition (e.g. +Node)
 	Fragments []*Fragment
 	Children  map[string]*ProjectNode
+	Parent    *ProjectNode
 }
 
 type Fragment struct {
 	File        string
 	Definitions []parser.Definition
-	IsObject    bool            // True if this fragment comes from an ObjectNode, False if from File/Package body
-	ObjectPos   parser.Position // Position of the object node if IsObject is true
+	IsObject    bool            
+	ObjectPos   parser.Position 
 }
 
 func NewProjectTree() *ProjectTree {
@@ -39,8 +48,37 @@ func NormalizeName(name string) string {
 	return name
 }
 
+func (pt *ProjectTree) RemoveFile(file string) {
+	// Remove references from this file
+	newRefs := []Reference{}
+	for _, ref := range pt.References {
+		if ref.File != file {
+			newRefs = append(newRefs, ref)
+		}
+	}
+	pt.References = newRefs
+
+	// Remove fragments from tree
+	pt.removeFileFromNode(pt.Root, file)
+}
+
+func (pt *ProjectTree) removeFileFromNode(node *ProjectNode, file string) {
+	newFragments := []*Fragment{}
+	for _, frag := range node.Fragments {
+		if frag.File != file {
+			newFragments = append(newFragments, frag)
+		}
+	}
+	node.Fragments = newFragments
+
+	for _, child := range node.Children {
+		pt.removeFileFromNode(child, file)
+	}
+}
+
 func (pt *ProjectTree) AddFile(file string, config *parser.Configuration) {
-	// Determine root node for this file based on package
+	pt.RemoveFile(file) // Ensure clean state for this file
+
 	node := pt.Root
 	if config.Package != nil {
 		parts := strings.Split(config.Package.URI, ".")
@@ -49,62 +87,42 @@ func (pt *ProjectTree) AddFile(file string, config *parser.Configuration) {
 			if part == "" {
 				continue
 			}
-			// Navigate or Create
 			if _, ok := node.Children[part]; !ok {
 				node.Children[part] = &ProjectNode{
 					Name:     part,
-					RealName: part, // Default, might be updated if we find a +Part later? 
-					// Actually, package segments are just names. 
-					// If they refer to an object defined elsewhere as +Part, we hope to match it.
+					RealName: part, 
 					Children: make(map[string]*ProjectNode),
+					Parent:   node,
 				}
 			}
 			node = node.Children[part]
 		}
 	}
 
-	// Now 'node' is the container for the file's definitions.
-	// We add a Fragment to this node containing the top-level definitions.
-	// But wait, definitions can be ObjectNodes (which start NEW nodes) or Fields (which belong to 'node').
-	
-	// We need to split definitions:
-	// Fields -> go into a Fragment for 'node'.
-	// ObjectNodes -> create/find Child node and add Fragment there.
-	
-	// Actually, the Build Process says: "#package ... implies all definitions ... are children".
-	// So if I have "Field = 1", it is a child of the package node.
-	// If I have "+Sub = {}", it is a child of the package node.
-	
-	// So we can just iterate definitions.
-	
-	// But for merging, we need to treat "+Sub" as a Node, not just a field.
-	
 	fileFragment := &Fragment{
-		File: file,
+		File:     file,
 		IsObject: false,
 	}
 	
 	for _, def := range config.Definitions {
 		switch d := def.(type) {
 		case *parser.Field:
-			// Fields belong to the current package node
 			fileFragment.Definitions = append(fileFragment.Definitions, d)
+			pt.indexValue(file, d.Value)
 		case *parser.ObjectNode:
-			// Object starts a new child node
 			norm := NormalizeName(d.Name)
 			if _, ok := node.Children[norm]; !ok {
 				node.Children[norm] = &ProjectNode{
 					Name:     norm,
 					RealName: d.Name,
 					Children: make(map[string]*ProjectNode),
+					Parent:   node,
 				}
 			}
 			child := node.Children[norm]
 			if child.RealName == norm && d.Name != norm {
-				child.RealName = d.Name // Update to specific name if we had generic
+				child.RealName = d.Name
 			}
-			
-			// Recursively add definitions of the object
 			pt.addObjectFragment(child, file, d)
 		}
 	}
@@ -125,6 +143,7 @@ func (pt *ProjectTree) addObjectFragment(node *ProjectNode, file string, obj *pa
 		switch d := def.(type) {
 		case *parser.Field:
 			frag.Definitions = append(frag.Definitions, d)
+			pt.indexValue(file, d.Value)
 		case *parser.ObjectNode:
 			norm := NormalizeName(d.Name)
 			if _, ok := node.Children[norm]; !ok {
@@ -132,6 +151,7 @@ func (pt *ProjectTree) addObjectFragment(node *ProjectNode, file string, obj *pa
 					Name:     norm,
 					RealName: d.Name,
 					Children: make(map[string]*ProjectNode),
+					Parent:   node,
 				}
 			}
 			child := node.Children[norm]
@@ -144,3 +164,93 @@ func (pt *ProjectTree) addObjectFragment(node *ProjectNode, file string, obj *pa
 	
 	node.Fragments = append(node.Fragments, frag)
 }
+
+func (pt *ProjectTree) indexValue(file string, val parser.Value) {
+	switch v := val.(type) {
+	case *parser.ReferenceValue:
+		pt.References = append(pt.References, Reference{
+			Name:     v.Value,
+			Position: v.Position,
+			File:     file,
+		})
+	case *parser.ArrayValue:
+		for _, elem := range v.Elements {
+			pt.indexValue(file, elem)
+		}
+	}
+}
+
+func (pt *ProjectTree) ResolveReferences() {
+	for i := range pt.References {
+		ref := &pt.References[i]
+		ref.Target = pt.findNode(pt.Root, ref.Name)
+	}
+}
+
+func (pt *ProjectTree) findNode(root *ProjectNode, name string) *ProjectNode {
+	if root.RealName == name || root.Name == name {
+		return root
+	}
+	for _, child := range root.Children {
+		if res := pt.findNode(child, name); res != nil {
+			return res
+		}
+	}
+	return nil
+}
+
+// QueryResult holds the result of a query at a position
+type QueryResult struct {
+	Node      *ProjectNode
+	Field     *parser.Field
+	Reference *Reference
+}
+
+func (pt *ProjectTree) Query(file string, line, col int) *QueryResult {
+	// 1. Check References
+	for i := range pt.References {
+		ref := &pt.References[i]
+		if ref.File == file {
+			// Check if pos is within reference range
+			// Approx length
+			if line == ref.Position.Line && col >= ref.Position.Column && col < ref.Position.Column+len(ref.Name) {
+				return &QueryResult{Reference: ref}
+			}
+		}
+	}
+
+	// 2. Check Definitions (traverse tree)
+	return pt.queryNode(pt.Root, file, line, col)
+}
+
+func (pt *ProjectTree) queryNode(node *ProjectNode, file string, line, col int) *QueryResult {
+	for _, frag := range node.Fragments {
+		if frag.File == file {
+			// Check Object definition itself
+			if frag.IsObject {
+				// Object definition usually starts at 'Name'.
+				// Position is start of Name.
+				if line == frag.ObjectPos.Line && col >= frag.ObjectPos.Column && col < frag.ObjectPos.Column+len(node.RealName) {
+					return &QueryResult{Node: node}
+				}
+			}
+			
+			// Check definitions in fragment
+			for _, def := range frag.Definitions {
+				if f, ok := def.(*parser.Field); ok {
+					// Check field name range
+					if line == f.Position.Line && col >= f.Position.Column && col < f.Position.Column+len(f.Name) {
+						return &QueryResult{Field: f}
+					}
+				}
+			}
+		}
+	}
+	
+	for _, child := range node.Children {
+		if res := pt.queryNode(child, file, line, col); res != nil {
+			return res
+		}
+	}
+	return nil
+}
diff --git a/internal/lsp/server.go b/internal/lsp/server.go
index ec11d48..0362dfa 100644
--- a/internal/lsp/server.go
+++ b/internal/lsp/server.go
@@ -6,6 +6,10 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"strings"
+
+	"github.com/marte-dev/marte-dev-tools/internal/index"
+	"github.com/marte-dev/marte-dev-tools/internal/parser"
 )
 
 type JsonRpcMessage struct {
@@ -22,6 +26,56 @@ type JsonRpcError struct {
 	Message string `json:"message"`
 }
 
+type DidOpenTextDocumentParams struct {
+	TextDocument TextDocumentItem `json:"textDocument"`
+}
+
+type DidChangeTextDocumentParams struct {
+	TextDocument   VersionedTextDocumentIdentifier `json:"textDocument"`
+	ContentChanges []TextDocumentContentChangeEvent `json:"contentChanges"`
+}
+
+type TextDocumentItem struct {
+	URI        string `json:"uri"`
+	LanguageID string `json:"languageId"`
+	Version    int    `json:"version"`
+	Text       string `json:"text"`
+}
+
+type VersionedTextDocumentIdentifier struct {
+	URI     string `json:"uri"`
+	Version int    `json:"version"`
+}
+
+type TextDocumentContentChangeEvent struct {
+	Text string `json:"text"`
+}
+
+type HoverParams struct {
+	TextDocument TextDocumentIdentifier `json:"textDocument"`
+	Position     Position               `json:"position"`
+}
+
+type TextDocumentIdentifier struct {
+	URI string `json:"uri"`
+}
+
+type Position struct {
+	Line      int `json:"line"`
+	Character int `json:"character"`
+}
+
+type Hover struct {
+	Contents interface{} `json:"contents"`
+}
+
+type MarkupContent struct {
+	Kind  string `json:"kind"`
+	Value string `json:"value"`
+}
+
+var tree = index.NewProjectTree()
+
 func RunServer() {
 	reader := bufio.NewReader(os.Stdin)
 	for {
@@ -39,7 +93,6 @@ func RunServer() {
 }
 
 func readMessage(reader *bufio.Reader) (*JsonRpcMessage, error) {
-	// LSP uses Content-Length header
 	var contentLength int
 	for {
 		line, err := reader.ReadString('\n')
@@ -74,9 +127,6 @@ func handleMessage(msg *JsonRpcMessage) {
 				"hoverProvider":    true,
 				"definitionProvider": true,
 				"referencesProvider": true,
-				"completionProvider": map[string]interface{}{
-					"triggerCharacters": []string{"=", ".", "{", "+", "$"},
-				},
 			},
 		})
 	case "initialized":
@@ -86,11 +136,102 @@ func handleMessage(msg *JsonRpcMessage) {
 	case "exit":
 		os.Exit(0)
 	case "textDocument/didOpen":
-		// Handle file open
+		var params DidOpenTextDocumentParams
+		if err := json.Unmarshal(msg.Params, &params); err == nil {
+			handleDidOpen(params)
+		}
 	case "textDocument/didChange":
-		// Handle file change
+		var params DidChangeTextDocumentParams
+		if err := json.Unmarshal(msg.Params, &params); err == nil {
+			handleDidChange(params)
+		}
 	case "textDocument/hover":
-		// Handle hover
+		var params HoverParams
+		if err := json.Unmarshal(msg.Params, &params); err == nil {
+			res := handleHover(params)
+			respond(msg.ID, res)
+		} else {
+			respond(msg.ID, nil)
+		}
+	}
+}
+
+func uriToPath(uri string) string {
+	return strings.TrimPrefix(uri, "file://")
+}
+
+func handleDidOpen(params DidOpenTextDocumentParams) {
+	path := uriToPath(params.TextDocument.URI)
+	p := parser.NewParser(params.TextDocument.Text)
+	config, err := p.Parse()
+	if err == nil {
+		tree.AddFile(path, config)
+		tree.ResolveReferences()
+	}
+}
+
+func handleDidChange(params DidChangeTextDocumentParams) {
+	if len(params.ContentChanges) == 0 {
+		return
+	}
+	// Full sync: text is in ContentChanges[0].Text
+	text := params.ContentChanges[0].Text
+	path := uriToPath(params.TextDocument.URI)
+	p := parser.NewParser(text)
+	config, err := p.Parse()
+	if err == nil {
+		tree.AddFile(path, config)
+		tree.ResolveReferences()
+	}
+}
+
+func handleHover(params HoverParams) *Hover {
+	path := uriToPath(params.TextDocument.URI)
+	// LSP 0-based to Parser 1-based
+	line := params.Position.Line + 1
+	col := params.Position.Character + 1
+	
+	res := tree.Query(path, line, col)
+	if res == nil {
+		return nil
+	}
+	
+	var content string
+	
+	if res.Node != nil {
+		// Try to find Class field
+		class := "Unknown"
+		for _, frag := range res.Node.Fragments {
+			for _, def := range frag.Definitions {
+				if f, ok := def.(*parser.Field); ok && f.Name == "Class" {
+					if s, ok := f.Value.(*parser.StringValue); ok {
+						class = s.Value
+					} else if r, ok := f.Value.(*parser.ReferenceValue); ok {
+						class = r.Value
+					}
+				}
+			}
+		}
+		content = fmt.Sprintf("**Object**: `%s`\n\n**Class**: `%s`", res.Node.RealName, class)
+	} else if res.Field != nil {
+		content = fmt.Sprintf("**Field**: `%s`", res.Field.Name)
+	} else if res.Reference != nil {
+		targetName := "Unresolved"
+		if res.Reference.Target != nil {
+			targetName = res.Reference.Target.RealName
+		}
+		content = fmt.Sprintf("**Reference**: `%s` -> `%s`", res.Reference.Name, targetName)
+	}
+	
+	if content == "" {
+		return nil
+	}
+	
+	return &Hover{
+		Contents: MarkupContent{
+			Kind:  "markdown",
+			Value: content,
+		},
 	}
 }
 
@@ -106,4 +247,4 @@ func respond(id interface{}, result interface{}) {
 func send(msg interface{}) {
 	body, _ := json.Marshal(msg)
 	fmt.Printf("Content-Length: %d\r\n\r\n%s", len(body), body)
-}
+}
\ No newline at end of file
diff --git a/mdt b/mdt
index 73ced4f..bbff76a 100755
Binary files a/mdt and b/mdt differ