diff --git a/tools/xcui/axtree.go b/tools/xcui/axtree.go
new file mode 100644
index 00000000..3f7e2b08
--- /dev/null
+++ b/tools/xcui/axtree.go
@@ -0,0 +1,65 @@
+package main
+
+import "encoding/json"
+
+// Frame is the numeric rect AXe emits alongside the string AXFrame.
+type Frame struct {
+	X      float64 `json:"x"`
+	Y      float64 `json:"y"`
+	Width  float64 `json:"width"`
+	Height float64 `json:"height"`
+}
+
+// AXElement mirrors one node of `axe describe-ui` output. Fields that AXe
+// emits as JSON null are pointers so absence is distinguishable from "".
+type AXElement struct {
+	AXUniqueID      *string     `json:"AXUniqueId"`
+	AXLabel         *string     `json:"AXLabel"`
+	AXValue         *string     `json:"AXValue"`
+	Title           *string     `json:"title"`
+	Help            *string     `json:"help"`
+	Subrole         *string     `json:"subrole"`
+	Role            string      `json:"role"`
+	RoleDescription string      `json:"role_description"`
+	Type            string      `json:"type"`
+	AXFrame         string      `json:"AXFrame"`
+	Frame           Frame       `json:"frame"`
+	Enabled         bool        `json:"enabled"`
+	PID             int         `json:"pid"`
+	Children        []AXElement `json:"children"`
+}
+
+func parseDescribeUI(data []byte) ([]AXElement, error) {
+	var roots []AXElement
+	if err := json.Unmarshal(data, &roots); err != nil {
+		return nil, err
+	}
+	return roots, nil
+}
+
+// walk visits every element depth-first, roots first.
+func walk(roots []AXElement, visit func(AXElement)) {
+	for _, el := range roots {
+		visit(el)
+		walk(el.Children, visit)
+	}
+}
+
+// findByID returns every element whose AXUniqueId equals id. More than one
+// match means the identifier isn't unique (the --single assertion catches it).
+func findByID(roots []AXElement, id string) []AXElement {
+	var out []AXElement
+	walk(roots, func(el AXElement) {
+		if el.AXUniqueID != nil && *el.AXUniqueID == id {
+			out = append(out, el)
+		}
+	})
+	return out
+}
+
+func deref(s *string) string {
+	if s == nil {
+		return ""
+	}
+	return *s
+}
diff --git a/tools/xcui/main_test.go b/tools/xcui/main_test.go
index c170fee4..48704b24 100644
--- a/tools/xcui/main_test.go
+++ b/tools/xcui/main_test.go
@@ -7,3 +7,60 @@ func TestVersionConstSet(t *testing.T) {
 		t.Fatal("version const must be set")
 	}
 }
+
+const sampleTree = `[
+  {
+    "AXUniqueId": null, "AXLabel": "App", "AXValue": null,
+    "role": "AXApplication", "type": "Application", "enabled": true,
+    "frame": {"x":0,"y":0,"width":402,"height":874},
+    "children": [
+      {
+        "AXUniqueId": "artist.hero", "AXLabel": "Artwork for The Chemical Brothers",
+        "AXValue": null, "role": "AXImage", "type": "Image", "enabled": true,
+        "frame": {"x":0,"y":0,"width":402,"height":402}, "children": []
+      },
+      {
+        "AXUniqueId": "play.all", "AXLabel": "Play all", "AXValue": null,
+        "role": "AXButton", "type": "Button", "enabled": true,
+        "frame": {"x":16,"y":420,"width":120,"height":44}, "children": []
+      }
+    ]
+  }
+]`
+
+func TestParseDescribeUI(t *testing.T) {
+	roots, err := parseDescribeUI([]byte(sampleTree))
+	if err != nil {
+		t.Fatalf("parse error: %v", err)
+	}
+	if len(roots) != 1 || len(roots[0].Children) != 2 {
+		t.Fatalf("got %d roots / %d children, want 1 / 2", len(roots), len(roots[0].Children))
+	}
+}
+
+func TestFindByID(t *testing.T) {
+	roots, _ := parseDescribeUI([]byte(sampleTree))
+	matches := findByID(roots, "artist.hero")
+	if len(matches) != 1 {
+		t.Fatalf("got %d matches, want 1", len(matches))
+	}
+	if got := deref(matches[0].AXLabel); got != "Artwork for The Chemical Brothers" {
+		t.Errorf("label = %q", got)
+	}
+}
+
+func TestFindByIDAbsent(t *testing.T) {
+	roots, _ := parseDescribeUI([]byte(sampleTree))
+	if matches := findByID(roots, "nope"); len(matches) != 0 {
+		t.Errorf("got %d matches, want 0", len(matches))
+	}
+}
+
+func FuzzParseDescribeUI(f *testing.F) {
+	f.Add([]byte(sampleTree))
+	f.Add([]byte(`[]`))
+	f.Add([]byte(`[{"AXUniqueId":null,"children":[]}]`))
+	f.Fuzz(func(t *testing.T, data []byte) {
+		_, _ = parseDescribeUI(data) // must not panic
+	})
+}