diff --git a/packages/doenetml-iframe/src/test-main.tsx b/packages/doenetml-iframe/src/test-main.tsx
index 24c09d84bb..59f1767fb6 100644
--- a/packages/doenetml-iframe/src/test-main.tsx
+++ b/packages/doenetml-iframe/src/test-main.tsx
@@ -23,12 +23,72 @@ const STANDALONE_CSS_BLOB_URL = URL.createObjectURL(
     new Blob([STANDALONE_CSS], { type: "text/css" }),
 );
 
+const SOURCE_STORAGE_KEY = "doenetml-iframe-dev-source";
+const SAVE_DEBOUNCE_MS = 500;
+
+const DEFAULT_EDITOR_SOURCE = `<mathInput /><p><mathInput />Use this to test DoenetML<mathInput /></p>
+                <problem copy="doenet:abcdef" />
+                <graph />
+                <graph />
+                <graph />
+               <mathInput />`;
+
+let saveTimer: number | null = null;
+
+function getInitialSource(): string {
+    try {
+        return (
+            localStorage.getItem(SOURCE_STORAGE_KEY) ?? DEFAULT_EDITOR_SOURCE
+        );
+    } catch {
+        return DEFAULT_EDITOR_SOURCE;
+    }
+}
+
+// Wired to the editor's immediate (per-keystroke) change callback, so debounce
+// the writes: calling localStorage.setItem synchronously on every keystroke can
+// noticeably block the UI for larger documents.
+let pendingSource: string | null = null;
+
+window.addEventListener("pagehide", () => {
+    if (pendingSource === null) {
+        return;
+    }
+    if (saveTimer !== null) {
+        window.clearTimeout(saveTimer);
+        saveTimer = null;
+    }
+    try {
+        localStorage.setItem(SOURCE_STORAGE_KEY, pendingSource);
+    } catch {
+        // Ignore localStorage failures in constrained environments.
+    }
+    pendingSource = null;
+});
+
+function saveSource(source: string) {
+    pendingSource = source;
+    if (saveTimer !== null) {
+        window.clearTimeout(saveTimer);
+    }
+    saveTimer = window.setTimeout(() => {
+        saveTimer = null;
+        try {
+            localStorage.setItem(SOURCE_STORAGE_KEY, source);
+        } catch {
+            // Ignore localStorage failures in constrained environments.
+        }
+        pendingSource = null;
+    }, SAVE_DEBOUNCE_MS);
+}
+
 const root = ReactDOM.createRoot(document.getElementById("root")!);
 root.render(<App />);
 
 function App() {
     const DOENET_LEGACY_VERSION = "0.6.5";
     const editorRef = useRef<DoenetEditorHandle>(null);
+    const [initialEditorSource] = React.useState(getInitialSource);
 
     return (
         <React.Fragment>
@@ -95,18 +155,14 @@ function App() {
             </div>
             <DoenetEditor
                 ref={editorRef}
-                doenetML={`<mathInput /><p><mathInput />Use this to test DoenetML<mathInput /></p>
-                <problem copy="doenet:abcdef" />
-                <graph />
-                <graph />
-                <graph />
-               <mathInput />`}
+                doenetML={initialEditorSource}
                 standaloneUrl={STANDALONE_BLOB_URL}
                 cssUrl={STANDALONE_CSS_BLOB_URL}
                 activityId={"a"}
                 showDiagnostics={true}
                 showResponses={false}
                 fetchExternalDoenetML={fetchExternalDoenetML}
+                immediateDoenetmlChangeCallback={saveSource}
             />
         </React.Fragment>
     );
diff --git a/packages/doenetml-iframe/vite.config.ts b/packages/doenetml-iframe/vite.config.ts
index c5e514f13c..22e651c4df 100644
--- a/packages/doenetml-iframe/vite.config.ts
+++ b/packages/doenetml-iframe/vite.config.ts
@@ -43,6 +43,9 @@ export default defineConfig({
         }),
         suppressLogPlugin(),
     ],
+    server: {
+        host: "0.0.0.0",
+    },
     build: {
         minify: false,
         outDir: "dist/component",
diff --git a/packages/standalone/index.html b/packages/standalone/index.html
index bee77c21ea..fd7f067d56 100644
--- a/packages/standalone/index.html
+++ b/packages/standalone/index.html
@@ -12,41 +12,41 @@
         <script></script>
         <div class="doenetml-viewer">
             <script type="text/doenetml">
-                <m>\frac{5}{6}</m>
-                <p>1+1=<answer>2</answer></p>
-                <graph>
+<m>\frac{5}{6}</m>
+<p>1+1=<answer>2</answer></p>
+<graph>
 
-                  <line through="(-8,8) (9,6)" />
-                  <line through="(0,4)" slope="1/2" styleNumber="2" />
+  <line through="(-8,8) (9,6)" />
+  <line through="(0,4)" slope="1/2" styleNumber="2" />
 
-                  <line equation="y=2x-8" styleNumber="3" />
-                  <line equation="x=-6" styleNumber="4" />
+  <line equation="y=2x-8" styleNumber="3" />
+  <line equation="x=-6" styleNumber="4" />
 
-                </graph>
+</graph>
             </script>
         </div>
         <div class="doenetml-viewer" data-doenet-read-only="true">
             <script type="text/doenetml">
-                <m>\frac{4}{5}</m>
-                <p>1+2=<answer>3</answer></p>
+<m>\frac{4}{5}</m>
+<p>1+2=<answer>3</answer></p>
 
-                <graph>
+<graph>
 
-                  <line through="(0,4)" slope="1/2" styleNumber="2" />
+  <line through="(0,4)" slope="1/2" styleNumber="2" />
 
-                </graph>
+</graph>
             </script>
         </div>
 
         <div class="doenetml-editor" data-doenet-height="600px">
             <script type="text/doenetml">
-                <m>\frac{3}{4}</m>
-                <p>1+3=<answer>4</answer></p>
-                <graph showNavigation="false">
+<m>\frac{3}{4}</m>
+<p>1+3=<answer>4</answer></p>
+<graph showNavigation="false">
 
-                  <line through="(-8,8) (9,6)" />
+  <line through="(-8,8) (9,6)" />
 
-                </graph>
+</graph>
             </script>
         </div>
     </body>
diff --git a/packages/standalone/src/test-main.tsx b/packages/standalone/src/test-main.tsx
index 81cff13ef2..ecff36c5af 100644
--- a/packages/standalone/src/test-main.tsx
+++ b/packages/standalone/src/test-main.tsx
@@ -7,13 +7,55 @@ import {
     renderDoenetEditorToContainer,
 } from "./index";
 
+const SOURCE_STORAGE_KEY_PREFIX = "doenetml-standalone-dev-source-";
+const SAVE_DEBOUNCE_MS = 500;
+
+const saveTimers = new Map<string, ReturnType<typeof window.setTimeout>>();
+
+// Wired to the editor's immediate (per-keystroke) change callback, so debounce
+// the writes: calling localStorage.setItem synchronously on every keystroke can
+// noticeably block the UI for larger documents.
+function saveSource(key: string, source: string) {
+    const pending = saveTimers.get(key);
+    if (pending !== undefined) {
+        window.clearTimeout(pending);
+    }
+    saveTimers.set(
+        key,
+        window.setTimeout(() => {
+            saveTimers.delete(key);
+            try {
+                localStorage.setItem(key, source);
+            } catch {
+                // Ignore localStorage failures in constrained environments.
+            }
+        }, SAVE_DEBOUNCE_MS),
+    );
+}
+
 document.addEventListener("DOMContentLoaded", () => {
     document.querySelectorAll(".doenetml-viewer").forEach((container) => {
         console.log("Rendering doenet viewer to container", container);
         renderDoenetViewerToContainer(container);
     });
-    document.querySelectorAll(".doenetml-editor").forEach((container) => {
-        console.log("Rendering doenet editor to container", container);
-        renderDoenetEditorToContainer(container);
-    });
+    document
+        .querySelectorAll(".doenetml-editor")
+        .forEach((container, index) => {
+            console.log("Rendering doenet editor to container", container);
+            const storageKey = `${SOURCE_STORAGE_KEY_PREFIX}${index}`;
+            let storedSource: string | null = null;
+            try {
+                storedSource = localStorage.getItem(storageKey);
+            } catch {
+                // Ignore localStorage failures in constrained environments.
+            }
+            renderDoenetEditorToContainer(
+                container,
+                storedSource ?? undefined,
+                {
+                    immediateDoenetmlChangeCallback: (source: string) =>
+                        saveSource(storageKey, source),
+                },
+            );
+        });
 });
diff --git a/packages/standalone/vite.config.ts b/packages/standalone/vite.config.ts
index 44154318ad..3c7bbe3202 100644
--- a/packages/standalone/vite.config.ts
+++ b/packages/standalone/vite.config.ts
@@ -21,6 +21,9 @@ export default defineConfig({
         }),
         suppressLogPlugin(),
     ],
+    server: {
+        host: "0.0.0.0",
+    },
     build: {
         minify: true,
         sourcemap: true,