diff --git a/src/components/App.tsx b/src/components/App.tsx
index 08d6784..8c684fd 100644
--- a/src/components/App.tsx
+++ b/src/components/App.tsx
@@ -37,7 +37,7 @@ class App extends React.Component<Props, State> {
 
       this.setState({ source: source, explain: explain, problem: "" });
     } catch (e) {
-      this.setState({ source: this.state.source, explain: null, problem: e });
+      this.setState({ source: this.state.source, explain: null, problem: e.message });
     }
   }
 
diff --git a/src/utils/GoFlow.test.tsx b/src/utils/GoFlow.test.tsx
new file mode 100644
index 0000000..bc59e58
--- /dev/null
+++ b/src/utils/GoFlow.test.tsx
@@ -0,0 +1,9 @@
+import { ReadSession } from './GoFlow';
+
+it('loads session from JSON', () => {
+    // loads when top-level object is session
+    expect(ReadSession('{"status": "complete", "runs": []}')).toMatchObject({ status: "complete", runs: [] });
+
+    // loads when session is nested object
+    expect(ReadSession('{"session": {"status": "complete", "runs": []}}')).toMatchObject({ status: "complete", runs: [] });
+})
\ No newline at end of file
diff --git a/src/utils/GoFlow.tsx b/src/utils/GoFlow.tsx
index d3f1d4d..691ecd3 100644
--- a/src/utils/GoFlow.tsx
+++ b/src/utils/GoFlow.tsx
@@ -49,6 +49,11 @@ export function ReadSession(src: string): Session {
         throw new Error(`invalid JSON: ${e}`);
     }
 
+    // could be an output from simulator which has nested session
+    if (typeof obj.session === "object") {
+        obj = obj.session
+    }
+
     if (!isSession(obj)) {
         throw new Error("not a valid session object")
     }