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250 lines
8.7 KiB
Markdown
250 lines
8.7 KiB
Markdown
# Widget Templates
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Minimal HTML scaffolds for the common widget shapes. Copy, fill in, ship.
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All templates inline the `App` class from `@modelcontextprotocol/ext-apps` at build time — the iframe's CSP blocks CDN script imports. They're intentionally framework-free; widgets are small enough that React/Vue hydration cost usually isn't worth it.
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---
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## Serving widget HTML
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Widgets are static HTML with one placeholder: `/*__EXT_APPS_BUNDLE__*/` gets replaced at server startup with the `ext-apps/app-with-deps` bundle (rewritten to expose `globalThis.ExtApps`).
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```typescript
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import { readFileSync } from "node:fs";
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import { createRequire } from "node:module";
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import { registerAppResource, RESOURCE_MIME_TYPE } from "@modelcontextprotocol/ext-apps/server";
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const require = createRequire(import.meta.url);
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const bundle = readFileSync(
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require.resolve("@modelcontextprotocol/ext-apps/app-with-deps"), "utf8",
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).replace(/export\{([^}]+)\};?\s*$/, (_, body) =>
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"globalThis.ExtApps={" +
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body.split(",").map((p) => {
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const [local, exported] = p.split(" as ").map((s) => s.trim());
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return `${exported ?? local}:${local}`;
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}).join(",") + "};",
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);
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const pickerHtml = readFileSync("./widgets/picker.html", "utf8")
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.replace("/*__EXT_APPS_BUNDLE__*/", () => bundle);
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registerAppResource(server, "Picker", "ui://widgets/picker.html", {},
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async () => ({
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contents: [{ uri: "ui://widgets/picker.html", mimeType: RESOURCE_MIME_TYPE, text: pickerHtml }],
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}),
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);
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```
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Bundle once per server startup (or at build time); reuse the `bundle` string across all widget templates.
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---
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## Picker (single-select list)
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```html
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<!doctype html>
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<meta charset="utf-8" />
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<style>
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body { font: 14px system-ui; margin: 0; }
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ul { list-style: none; padding: 0; margin: 0; max-height: 280px; overflow-y: auto; }
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li { padding: 10px 14px; cursor: pointer; border-bottom: 1px solid #eee; }
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li:hover { background: #f5f5f5; }
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.sub { color: #666; font-size: 12px; }
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</style>
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<ul id="list"></ul>
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<script type="module">
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/*__EXT_APPS_BUNDLE__*/
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const { App } = globalThis.ExtApps;
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(async () => {
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const app = new App({ name: "Picker", version: "1.0.0" }, {});
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const ul = document.getElementById("list");
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app.ontoolresult = ({ content }) => {
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const { items } = JSON.parse(content[0].text);
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ul.innerHTML = "";
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for (const it of items) {
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const li = document.createElement("li");
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li.innerHTML = `<div>${it.label}</div><div class="sub">${it.sub ?? ""}</div>`;
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li.addEventListener("click", () => {
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app.sendMessage({
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role: "user",
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content: [{ type: "text", text: `Selected: ${it.id}` }],
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});
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});
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ul.append(li);
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}
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};
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await app.connect();
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})();
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</script>
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```
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**Tool returns:** `{ content: [{ type: "text", text: JSON.stringify({ items: [{ id, label, sub? }] }) }] }`
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---
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## Confirm dialog
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```html
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<!doctype html>
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<meta charset="utf-8" />
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<style>
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body { font: 14px system-ui; margin: 16px; }
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.actions { display: flex; gap: 8px; margin-top: 16px; }
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button { padding: 8px 16px; cursor: pointer; }
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.danger { background: #d33; color: white; border: none; }
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</style>
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<p id="msg"></p>
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<div class="actions">
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<button id="cancel">Cancel</button>
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<button id="confirm" class="danger">Confirm</button>
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</div>
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<script type="module">
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/*__EXT_APPS_BUNDLE__*/
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const { App } = globalThis.ExtApps;
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(async () => {
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const app = new App({ name: "Confirm", version: "1.0.0" }, {});
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app.ontoolresult = ({ content }) => {
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const { message, confirmLabel } = JSON.parse(content[0].text);
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document.getElementById("msg").textContent = message;
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if (confirmLabel) document.getElementById("confirm").textContent = confirmLabel;
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};
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await app.connect();
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document.getElementById("confirm").addEventListener("click", () => {
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app.sendMessage({ role: "user", content: [{ type: "text", text: "Confirmed." }] });
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});
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document.getElementById("cancel").addEventListener("click", () => {
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app.sendMessage({ role: "user", content: [{ type: "text", text: "Cancelled." }] });
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});
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})();
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</script>
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```
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**Tool returns:** `{ content: [{ type: "text", text: JSON.stringify({ message, confirmLabel? }) }] }`
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**Note:** For simple confirmation, prefer **elicitation** over a widget — see `../build-mcp-server/references/elicitation.md`. Use this widget when you need custom styling or context beyond what a native form offers.
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---
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## Progress (long-running)
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```html
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<!doctype html>
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<meta charset="utf-8" />
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<style>
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body { font: 14px system-ui; margin: 16px; }
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.bar { height: 8px; background: #eee; border-radius: 4px; overflow: hidden; }
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.fill { height: 100%; background: #2a7; transition: width 200ms; }
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</style>
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<p id="label">Starting…</p>
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<div class="bar"><div id="fill" class="fill" style="width:0%"></div></div>
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<script type="module">
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/*__EXT_APPS_BUNDLE__*/
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const { App } = globalThis.ExtApps;
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(async () => {
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const app = new App({ name: "Progress", version: "1.0.0" }, {});
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const label = document.getElementById("label");
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const fill = document.getElementById("fill");
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// The tool result fires when the job completes — intermediate updates
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// arrive via the same handler if the server streams them
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app.ontoolresult = ({ content }) => {
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const state = JSON.parse(content[0].text);
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if (state.progress !== undefined) {
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label.textContent = state.message ?? `${state.progress}/${state.total}`;
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fill.style.width = `${(state.progress / state.total) * 100}%`;
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}
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if (state.done) {
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label.textContent = "Complete";
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fill.style.width = "100%";
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}
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};
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await app.connect();
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})();
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</script>
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```
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Server side, emit progress via `extra.sendNotification({ method: "notifications/progress", ... })` — see `apps-sdk-messages.md`.
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---
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## Display-only (chart / preview)
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Display widgets don't call `sendMessage` — they render and sit there. The tool should return a text summary **alongside** the widget so Claude can keep reasoning while the user sees the visual:
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```typescript
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registerAppTool(server, "show_chart", {
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description: "Render a revenue chart",
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inputSchema: { range: z.enum(["week", "month", "year"]) },
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_meta: { ui: { resourceUri: "ui://widgets/chart.html" } },
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}, async ({ range }) => {
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const data = await fetchRevenue(range);
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return {
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content: [{
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type: "text",
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text: `Revenue is up ${data.change}% over the ${range}. Chart rendered.\n\n` +
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JSON.stringify(data.points),
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}],
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};
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});
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```
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```html
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<!doctype html>
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<meta charset="utf-8" />
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<style>body { font: 14px system-ui; margin: 12px; }</style>
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<canvas id="chart" width="400" height="200"></canvas>
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<script type="module">
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/*__EXT_APPS_BUNDLE__*/
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const { App } = globalThis.ExtApps;
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(async () => {
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const app = new App({ name: "Chart", version: "1.0.0" }, {});
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app.ontoolresult = ({ content }) => {
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// Parse the JSON points from the text content (after the summary line)
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const text = content[0].text;
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const jsonStart = text.indexOf("\n\n") + 2;
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const points = JSON.parse(text.slice(jsonStart));
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drawChart(document.getElementById("chart"), points);
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};
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await app.connect();
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function drawChart(canvas, points) { /* ... */ }
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})();
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</script>
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```
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---
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## Carousel (multi-item display with actions)
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For presenting multiple items (product picks, search results) in a horizontal scroll rail. Patterns that tested well:
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- **Skip nav chevrons** — users know how to scroll. `scroll-snap-type` can cause a few-px-off-flush initial render; omit it and `scrollLeft = 0` after rendering.
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- **Layout-fork by item count** — `items.length === 1` → detail/PDP layout, `> 1` → carousel. Handle in widget JS, keep the tool schema flat.
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- **Put Claude's reasoning in each item** — a `note` field rendered as a small callout on the card gives users the "why" inline.
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- **Silent state via `updateModelContext`** — cart/selection changes should inform Claude without spamming the chat. Reserve `sendMessage` for terminal actions ("checkout", "done").
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- **Outbound links via `app.openLink`** — `window.open` and `<a target="_blank">` are blocked by the sandbox.
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```html
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<style>
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.rail { display: flex; gap: 10px; overflow-x: auto; padding: 12px; scrollbar-width: none; }
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.rail::-webkit-scrollbar { display: none; }
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.card { flex: 0 0 220px; border: 1px solid #ddd; border-radius: 6px; padding: 10px; }
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.thumb-box { aspect-ratio: 1 / 1; display: grid; place-items: center; background: #f7f8f8; }
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.thumb { max-width: 100%; max-height: 100%; object-fit: contain; }
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.note { font-size: 12px; color: #666; border-left: 3px solid orange; padding: 2px 8px; margin: 8px 0; }
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</style>
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<div class="rail" id="rail"></div>
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```
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**Images:** the iframe CSP blocks remote `img-src`. Fetch thumbnails server-side in the tool handler, embed as `data:` URLs in the JSON payload, and render from those. Add `referrerpolicy="no-referrer"` as a fallback.
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