diff --git a/src/__tests__/unit/components/graph-explorer/GraphLegend.test.tsx b/src/__tests__/unit/components/graph-explorer/GraphLegend.test.tsx
new file mode 100644
index 0000000000..6d663455df
--- /dev/null
+++ b/src/__tests__/unit/components/graph-explorer/GraphLegend.test.tsx
@@ -0,0 +1,83 @@
+// @vitest-environment jsdom
+import React from "react";
+import { render, screen, within } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+import { describe, test, expect } from "vitest";
+import { GraphLegend } from "@/components/graph-explorer/GraphLegend";
+import { getNodeColor } from "@/components/graph/graphUtils";
+
+describe("GraphLegend", () => {
+  test("renders nothing for an empty node list", () => {
+    const { container } = render(<GraphLegend nodes={[]} />);
+    expect(container).toBeEmptyDOMElement();
+  });
+
+  test("aggregates per-type counts and sorts descending", () => {
+    render(
+      <GraphLegend
+        nodes={[
+          { type: "File" },
+          { type: "Function" },
+          { type: "File" },
+          { type: "Function" },
+          { type: "File" },
+        ]}
+      />
+    );
+
+    const fileEntry = screen.getByTestId("graph-legend-entry-File");
+    const functionEntry = screen.getByTestId("graph-legend-entry-Function");
+
+    expect(within(fileEntry).getByText("3")).toBeInTheDocument();
+    expect(within(functionEntry).getByText("2")).toBeInTheDocument();
+
+    // "File" (count 3) should come before "Function" (count 2) in the DOM.
+    const entries = screen.getAllByTestId(/^graph-legend-entry-/);
+    expect(entries[0]).toBe(fileEntry);
+    expect(entries[1]).toBe(functionEntry);
+  });
+
+  test("toggle button collapses and expands the list, updating aria-expanded", async () => {
+    const user = userEvent.setup();
+    render(<GraphLegend nodes={[{ type: "File" }]} />);
+
+    const toggle = screen.getByTestId("graph-legend-toggle");
+    expect(toggle).toHaveAttribute("aria-expanded", "true");
+    expect(screen.getByTestId("graph-legend-entry-File")).toBeInTheDocument();
+
+    await user.click(toggle);
+    expect(toggle).toHaveAttribute("aria-expanded", "false");
+    expect(screen.queryByTestId("graph-legend-entry-File")).not.toBeInTheDocument();
+
+    await user.click(toggle);
+    expect(toggle).toHaveAttribute("aria-expanded", "true");
+    expect(screen.getByTestId("graph-legend-entry-File")).toBeInTheDocument();
+  });
+
+  test("swatch color matches getNodeColor for a listed and an unlisted type", () => {
+    const colorMap = { File: "#123456" };
+    render(
+      <GraphLegend nodes={[{ type: "File" }, { type: "Mystery" }]} colorMap={colorMap} />
+    );
+
+    const fileEntry = screen.getByTestId("graph-legend-entry-File");
+    const mysteryEntry = screen.getByTestId("graph-legend-entry-Mystery");
+
+    const fileSwatch = fileEntry.querySelector("span[style]") as HTMLElement;
+    const mysterySwatch = mysteryEntry.querySelector("span[style]") as HTMLElement;
+
+    expect(fileSwatch.style.backgroundColor).toBe(rgbFromHex(getNodeColor("File", colorMap)));
+    expect(mysterySwatch.style.backgroundColor).toBe(
+      rgbFromHex(getNodeColor("Mystery", colorMap))
+    );
+  });
+});
+
+/** jsdom normalizes inline hex colors to rgb() when read back from style. */
+function rgbFromHex(hex: string): string {
+  const value = hex.replace("#", "");
+  const r = parseInt(value.substring(0, 2), 16);
+  const g = parseInt(value.substring(2, 4), 16);
+  const b = parseInt(value.substring(4, 6), 16);
+  return `rgb(${r}, ${g}, ${b})`;
+}
diff --git a/src/components/graph-explorer/Graph2DView.tsx b/src/components/graph-explorer/Graph2DView.tsx
index e0da39600d..67c5c95a2d 100644
--- a/src/components/graph-explorer/Graph2DView.tsx
+++ b/src/components/graph-explorer/Graph2DView.tsx
@@ -2,6 +2,7 @@
 
 import React, { useEffect, useMemo, useRef, useState } from "react";
 import { GraphVisualization } from "@/components/graph/GraphVisualization";
+import { GraphLegend } from "./GraphLegend";
 import type { GraphEdge, GraphNode } from "@/components/graph/graphUtils";
 import { GRAPH_EXPLORER_COLORS } from "./nodeColors";
 import { LEGAL_NODE_ICONS, resolveEdgeStyle } from "./legalGraphStyles";
@@ -71,18 +72,21 @@ export function Graph2DView({
   );
 
   return (
-    <div ref={containerRef} className="h-full w-full" data-testid="graph-2d-view">
+    <div ref={containerRef} className="relative h-full w-full" data-testid="graph-2d-view">
       {size && nodes.length > 0 && (
-        <GraphVisualization
-          nodes={nodes}
-          edges={edges}
-          width={size.width}
-          height={size.height}
-          colorMap={GRAPH_EXPLORER_COLORS}
-          onNodeClick={handleNodeClick}
-          iconMap={LEGAL_NODE_ICONS}
-          edgeStyleFn={resolveEdgeStyle}
-        />
+        <>
+          <GraphVisualization
+            nodes={nodes}
+            edges={edges}
+            width={size.width}
+            height={size.height}
+            colorMap={GRAPH_EXPLORER_COLORS}
+            onNodeClick={handleNodeClick}
+            iconMap={LEGAL_NODE_ICONS}
+            edgeStyleFn={resolveEdgeStyle}
+          />
+          <GraphLegend nodes={nodes} colorMap={GRAPH_EXPLORER_COLORS} />
+        </>
       )}
     </div>
   );
diff --git a/src/components/graph-explorer/GraphLegend.tsx b/src/components/graph-explorer/GraphLegend.tsx
new file mode 100644
index 0000000000..95e7ac35db
--- /dev/null
+++ b/src/components/graph-explorer/GraphLegend.tsx
@@ -0,0 +1,74 @@
+"use client";
+
+import React, { useState } from "react";
+import { ChevronDown, ChevronUp } from "lucide-react";
+import { Card } from "@/components/ui/card";
+import { Button } from "@/components/ui/button";
+import { Badge } from "@/components/ui/badge";
+import { getNodeColor, type GraphNode } from "@/components/graph/graphUtils";
+
+/**
+ * Small overlay explaining what the 2D graph's node colors mean.
+ *
+ * Renders nothing when there are no nodes to summarize, so it never occupies
+ * layout space (or shows an empty card) before the graph has data.
+ */
+export function GraphLegend({
+  nodes,
+  colorMap,
+}: {
+  nodes: Pick<GraphNode, "type">[];
+  colorMap?: Record<string, string>;
+}) {
+  const [expanded, setExpanded] = useState(true);
+
+  const counts = new Map<string, number>();
+  for (const node of nodes) {
+    counts.set(node.type, (counts.get(node.type) ?? 0) + 1);
+  }
+
+  const entries = Array.from(counts.entries()).sort((a, b) => b[1] - a[1]);
+
+  if (entries.length === 0) {
+    return null;
+  }
+
+  return (
+    <Card className="absolute bottom-4 right-4 max-w-[220px] max-h-[60%] overflow-y-auto p-2 gap-1">
+      <Button
+        type="button"
+        variant="ghost"
+        size="sm"
+        aria-expanded={expanded}
+        data-testid="graph-legend-toggle"
+        className="flex w-full items-center justify-between px-2"
+        onClick={() => setExpanded((prev) => !prev)}
+      >
+        <span className="text-xs font-medium">Legend</span>
+        {expanded ? (
+          <ChevronDown className="size-3.5" />
+        ) : (
+          <ChevronUp className="size-3.5" />
+        )}
+      </Button>
+      {expanded && (
+        <ul className="flex flex-col gap-1 px-2 pb-1">
+          {entries.map(([type, count]) => (
+            <li
+              key={type}
+              data-testid={`graph-legend-entry-${type}`}
+              className="flex items-center gap-2 text-xs"
+            >
+              <span
+                className="inline-block size-2.5 shrink-0 rounded-full"
+                style={{ backgroundColor: getNodeColor(type, colorMap) }}
+              />
+              <span className="flex-1 truncate">{type}</span>
+              <Badge variant="secondary">{count}</Badge>
+            </li>
+          ))}
+        </ul>
+      )}
+    </Card>
+  );
+}