diff --git a/fstree.go b/fstree.go
new file mode 100644
index 0000000..760ed3c
--- /dev/null
+++ b/fstree.go
@@ -0,0 +1,114 @@
+/*
+This file contains the implementation of an in-memory tree of files and folders that the app used.
+It is initialised at startup and used for state changes in UI and later persisted to disk.
+
+- ruinivist, 30Dec25
+*/
+
+package main
+
+import (
+	"errors"
+	"path/filepath"
+)
+
+// enums for node types
+type FsNodeType int
+
+const (
+	FileNode FsNodeType = iota
+	FolderNode
+)
+
+// ==================== FsNode definition ====================
+// a single node, Fs => deals with file system related info mostly
+// a name for example can be content derived as well
+type FsNode struct {
+	nodeType FsNodeType
+	path     string
+	children []*FsNode
+	parent   *FsNode // for fast traversal up the tree
+	// for view layer
+	expanded bool
+}
+
+func (n *FsNode) FileName() string {
+	return filepath.Base(n.path)
+}
+
+// ==================== FsNode definition ====================
+
+// ==================== FsTree definition ====================
+type FsTree interface {
+	CreateNode(parent *FsNode, name string, nodeType FsNodeType) error
+	DeleteNode(node *FsNode) error
+	ToggleExpand(node *FsNode) error
+}
+
+// reminder: a bit redundant but I this above shows what funcs are there at a glace
+// so I still like to use this pattern ( 30Dec25)
+type FsTreeImpl struct {
+	root *FsNode
+}
+
+func NewFsTree(rootPath string) *FsTreeImpl {
+	return &FsTreeImpl{
+		root: &FsNode{
+			nodeType: FolderNode,
+			path:     rootPath,
+			children: make([]*FsNode, 0),
+			expanded: true,
+		},
+	}
+}
+
+func (t *FsTreeImpl) CreateNode(parent *FsNode, name string, nodeType FsNodeType) error {
+	if parent == nil {
+		return errors.New("parent node cannot be nil")
+	}
+	if parent.nodeType != FolderNode {
+		return errors.New("can only add nodes to folder nodes")
+	}
+	if name == "" {
+		return errors.New("node name cannot be empty")
+	}
+
+	newNode := &FsNode{
+		nodeType: nodeType,
+		path:     filepath.Join(parent.path, name),
+		children: make([]*FsNode, 0),
+		parent:   parent,
+		expanded: false,
+	}
+
+	parent.children = append(parent.children, newNode)
+	return nil
+}
+
+func (t *FsTreeImpl) DeleteNode(node *FsNode) error {
+	if node == nil {
+		return errors.New("node to delete cannot be nil")
+	}
+	parent := node.parent
+	if parent == nil {
+		return errors.New("node to delete must have a parent")
+	}
+
+	parent.children = RemoveFromSlice(parent.children, node)
+	return nil
+}
+
+// ToggleExpand toggles the expanded state of a node
+func (t *FsTreeImpl) ToggleExpand(node *FsNode) error {
+	if node == nil {
+		return errors.New("node cannot be nil")
+	}
+	if node.nodeType != FolderNode {
+		return errors.New("only folder nodes can be expanded or collapsed")
+	}
+
+	node.expanded = !node.expanded
+	return nil
+}
+
+// ==================== FsTree definition ====================
diff --git a/fstree_test.go b/fstree_test.go
new file mode 100644
index 0000000..f840477
--- /dev/null
+++ b/fstree_test.go
@@ -0,0 +1,280 @@
+/*
+This file is almost entirely ae ayee generated. That's one of the
+few good uses of ae ayee in my opinion
+
+- ruinivist, 30Dec25
+*/
+
+package main
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+func TestFsNode_FileName(t *testing.T) {
+	tests := []struct {
+		name     string
+		path     string
+		expected string
+	}{
+		{
+			name:     "simple filename",
+			path:     "/home/user/test.txt",
+			expected: "test.txt",
+		},
+		{
+			name:     "folder name",
+			path:     "/home/user/folder",
+			expected: "folder",
+		},
+		{
+			name:     "root path",
+			path:     "/",
+			expected: "/",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			node := &FsNode{path: tt.path}
+			got := node.FileName()
+			if got != tt.expected {
+				t.Errorf("FileName() = %q, want %q", got, tt.expected)
+			}
+		})
+	}
+}
+
+func TestNewFsTree(t *testing.T) {
+	rootPath := "/home/test"
+	tree := NewFsTree(rootPath)
+
+	if tree == nil {
+		t.Fatal("NewFsTree() returned nil")
+	}
+	if tree.root == nil {
+		t.Fatal("tree.root is nil")
+	}
+	if tree.root.nodeType != FolderNode {
+		t.Errorf("root nodeType = %v, want %v", tree.root.nodeType, FolderNode)
+	}
+	if tree.root.path != rootPath {
+		t.Errorf("root path = %q, want %q", tree.root.path, rootPath)
+	}
+	if !tree.root.expanded {
+		t.Error("root should be expanded by default")
+	}
+	if tree.root.children == nil {
+		t.Error("root children slice should be initialized")
+	}
+}
+
+func TestFsTreeImpl_CreateNode(t *testing.T) {
+	t.Run("create file node successfully", func(t *testing.T) {
+		tree := NewFsTree("/home/test")
+		err := tree.CreateNode(tree.root, "file.txt", FileNode)
+		if err != nil {
+			t.Fatalf("CreateNode() error = %v, want nil", err)
+		}
+		if len(tree.root.children) != 1 {
+			t.Fatalf("children count = %d, want 1", len(tree.root.children))
+		}
+
+		child := tree.root.children[0]
+		if child.nodeType != FileNode {
+			t.Errorf("child nodeType = %v, want %v", child.nodeType, FileNode)
+		}
+		expectedPath := filepath.Join("/home/test", "file.txt")
+		if child.path != expectedPath {
+			t.Errorf("child path = %q, want %q", child.path, expectedPath)
+		}
+		if child.parent != tree.root {
+			t.Error("child parent should point to root")
+		}
+		if child.expanded {
+			t.Error("new node should not be expanded by default")
+		}
+	})
+
+	t.Run("create folder node successfully", func(t *testing.T) {
+		tree := NewFsTree("/home/test")
+		err := tree.CreateNode(tree.root, "subfolder", FolderNode)
+		if err != nil {
+			t.Fatalf("CreateNode() error = %v, want nil", err)
+		}
+		if len(tree.root.children) != 1 {
+			t.Fatalf("children count = %d, want 1", len(tree.root.children))
+		}
+
+		child := tree.root.children[0]
+		if child.nodeType != FolderNode {
+			t.Errorf("child nodeType = %v, want %v", child.nodeType, FolderNode)
+		}
+	})
+
+	t.Run("error when parent is nil", func(t *testing.T) {
+		tree := NewFsTree("/home/test")
+		err := tree.CreateNode(nil, "file.txt", FileNode)
+		if err == nil {
+			t.Fatal("CreateNode() with nil parent should return error")
+		}
+		if err.Error() != "parent node cannot be nil" {
+			t.Errorf("error message = %q, want %q", err.Error(), "parent node cannot be nil")
+		}
+	})
+
+	t.Run("error when parent is file node", func(t *testing.T) {
+		tree := NewFsTree("/home/test")
+		fileNode := &FsNode{
+			nodeType: FileNode,
+			path:     "/home/test/file.txt",
+			parent:   tree.root,
+		}
+		err := tree.CreateNode(fileNode, "child.txt", FileNode)
+		if err == nil {
+			t.Fatal("CreateNode() with file parent should return error")
+		}
+		if err.Error() != "can only add nodes to folder nodes" {
+			t.Errorf("error message = %q, want %q", err.Error(), "can only add nodes to folder nodes")
+		}
+	})
+
+	t.Run("error when name is empty", func(t *testing.T) {
+		tree := NewFsTree("/home/test")
+		err := tree.CreateNode(tree.root, "", FileNode)
+		if err == nil {
+			t.Fatal("CreateNode() with empty name should return error")
+		}
+		if err.Error() != "node name cannot be empty" {
+			t.Errorf("error message = %q, want %q", err.Error(), "node name cannot be empty")
+		}
+	})
+
+	t.Run("create nested nodes", func(t *testing.T) {
+		tree := NewFsTree("/home/test")
+		err := tree.CreateNode(tree.root, "folder1", FolderNode)
+		if err != nil {
+			t.Fatalf("CreateNode() error = %v", err)
+		}
+		folder1 := tree.root.children[0]
+
+		err = tree.CreateNode(folder1, "file.txt", FileNode)
+		if err != nil {
+			t.Fatalf("CreateNode() error = %v", err)
+		}
+
+		if len(folder1.children) != 1 {
+			t.Fatalf("folder1 children count = %d, want 1", len(folder1.children))
+		}
+		expectedPath := filepath.Join("/home/test", "folder1", "file.txt")
+		if folder1.children[0].path != expectedPath {
+			t.Errorf("nested file path = %q, want %q", folder1.children[0].path, expectedPath)
+		}
+	})
+}
+
+func TestFsTreeImpl_DeleteNode(t *testing.T) {
+	t.Run("delete node successfully", func(t *testing.T) {
+		tree := NewFsTree("/home/test")
+		tree.CreateNode(tree.root, "file1.txt", FileNode)
+		tree.CreateNode(tree.root, "file2.txt", FileNode)
+
+		if len(tree.root.children) != 2 {
+			t.Fatalf("initial children count = %d, want 2", len(tree.root.children))
+		}
+
+		nodeToDelete := tree.root.children[0]
+		err := tree.DeleteNode(nodeToDelete)
+		if err != nil {
+			t.Fatalf("DeleteNode() error = %v, want nil", err)
+		}
+
+		if len(tree.root.children) != 1 {
+			t.Errorf("children count after delete = %d, want 1", len(tree.root.children))
+		}
+	})
+
+	t.Run("error when node is nil", func(t *testing.T) {
+		tree := NewFsTree("/home/test")
+		err := tree.DeleteNode(nil)
+		if err == nil {
+			t.Fatal("DeleteNode() with nil node should return error")
+		}
+		if err.Error() != "node to delete cannot be nil" {
+			t.Errorf("error message = %q, want %q", err.Error(), "node to delete cannot be nil")
+		}
+	})
+
+	t.Run("error when node has no parent", func(t *testing.T) {
+		tree := NewFsTree("/home/test")
+		orphanNode := &FsNode{
+			nodeType: FileNode,
+			path:     "/orphan.txt",
+			parent:   nil,
+		}
+		err := tree.DeleteNode(orphanNode)
+		if err == nil {
+			t.Fatal("DeleteNode() with no parent should return error")
+		}
+		if err.Error() != "node to delete must have a parent" {
+			t.Errorf("error message = %q, want %q", err.Error(), "node to delete must have a parent")
+		}
+	})
+}
+
+func TestFsTreeImpl_ToggleExpand(t *testing.T) {
+	t.Run("toggle folder expansion", func(t *testing.T) {
+		tree := NewFsTree("/home/test")
+		tree.CreateNode(tree.root, "folder1", FolderNode)
+		folder := tree.root.children[0]
+
+		// Initially not expanded
+		if folder.expanded {
+			t.Error("new folder should not be expanded")
+		}
+
+		// Toggle to expanded
+		err := tree.ToggleExpand(folder)
+		if err != nil {
+			t.Fatalf("ToggleExpand() error = %v", err)
+		}
+		if !folder.expanded {
+			t.Error("folder should be expanded after toggle")
+		}
+
+		// Toggle back to collapsed
+		err = tree.ToggleExpand(folder)
+		if err != nil {
+			t.Fatalf("ToggleExpand() error = %v", err)
+		}
+		if folder.expanded {
+			t.Error("folder should be collapsed after second toggle")
+		}
+	})
+
+	t.Run("error when node is nil", func(t *testing.T) {
+		tree := NewFsTree("/home/test")
+		err := tree.ToggleExpand(nil)
+		if err == nil {
+			t.Fatal("ToggleExpand() with nil node should return error")
+		}
+		if err.Error() != "node cannot be nil" {
+			t.Errorf("error message = %q, want %q", err.Error(), "node cannot be nil")
+		}
+	})
+
+	t.Run("error when node is file", func(t *testing.T) {
+		tree := NewFsTree("/home/test")
+		tree.CreateNode(tree.root, "file.txt", FileNode)
+		fileNode := tree.root.children[0]
+
+		err := tree.ToggleExpand(fileNode)
+		if err == nil {
+			t.Fatal("ToggleExpand() on file node should return error")
+		}
+		if err.Error() != "only folder nodes can be expanded or collapsed" {
+			t.Errorf("error message = %q, want %q", err.Error(), "only folder nodes can be expanded or collapsed")
+		}
+	})
+}