Scarf Miniapp Author

Scarf Mini-App Author

Build a mini-app: a small web surface (HTML/CSS/JS) that Scarf renders inside a project's cockpit (the "Mini-apps" panel) over a narrow, versioned JS bridge (window.scarf). A mini-app is a project facet — it lives in the project directory and is bound to the project (and, for scarf.prompt, a dedicated Hermes agent session). Because it's plain web + a tiny API, you can author one reliably with your file tools.

When to invoke this skill

• "Build me a mini-app that …" / "Add a little app to this project for …"
• "Make a panel that shows / lets me …" (a task list, an approval queue, a status board, a chart, a form).
• During a project upgrade (the scarf-template-author upgrade flow), to add a starter mini-app or two.

Do not invoke for: editing the project's dashboard.json (that's the Dashboard panel — use widgets), or pure reference questions (answer inline from below).

Where a mini-app lives

<project>/.scarf/miniapps/<id>/
├── miniapp.json     # manifest (REQUIRED)
├── index.html       # entry document (REQUIRED; default entry name)
└── …                # any local CSS/JS/images, referenced by RELATIVE path

• <id> is the directory name and is canonical — it must equal miniapp.json.id. Use a short kebab-case slug (e.g. task-board).
• Scarf discovers the mini-app automatically once the dir + miniapp.json exist; no registration step.

The manifest — miniapp.json

{
  "id": "task-board",
  "name": "Task Board",
  "version": "1.0.0",
  "entry": "index.html",
  "minBridgeVersion": "1.0",
  "permissions": ["query:kanban.tasks"],
  "panelHint": { "preferredWidth": 480, "placement": "panel" },
  "generated": true
}

• Only id + name are required; entry defaults to index.html, permissions to [] (default-deny), minBridgeVersion to "1.0", generated to false.
• Set "generated": true for anything you author — it labels the app as agent-written in the cockpit and on the permission sheet. It no longer buys or costs permissions (sensitive ones are off for everyone), so claiming otherwise gains nothing; be honest.
• permissions must list every bridge surface the app uses (default-deny — an undeclared call is refused).
• Raise minBridgeVersion only for a surface you actually need — "1.1" for scarf.openURL. An older Scarf refuses the app outright rather than half-running it.

The bridge — window.scarf (injected at document start; current version 1.1)

scarf.context and scarf.version are synchronous (baked in at load). Everything else is async (returns a Promise). Each async call is permission-checked host-side; a missing permission rejects.

† Sensitive permissions (prompt, net, file:read, file:write, kanban:write, and any unknown or non-allow-listed query:<kind>) start OFF in the permission sheet for every app, generated or not, until the user ticks them. Non-sensitive ones (store, events, query:kanban.tasks, open_url) start on. Prefer non-sensitive surfaces so your app works immediately; only request prompt (and friends) when the app genuinely needs to drive the agent, and tell the user they'll be asked to grant it.

net, file:write, and kanban:write (move/create) are not wired in this build — don't rely on them. There is no external network: CSP blocks it and there's no net surface, so bundle everything locally (inline CSS/JS or local files; no CDNs, no fetch() to the internet).

External links — use open_url, never a bare <a>

There is no browser inside the mini-app. Navigation is locked to scarf-miniapp://, so <a href="https://…"> — with or without target="_blank" — is a dead link: the click is blocked and the user gets nothing. Don't write one and don't fake one with window.open.

If your app shows links (an article list, a docs shortcut, a search result):

1. Declare "open_url" in permissions and set "minBridgeVersion": "1.1".
2. Render the link as a button/anchor with your own click handler and call scarf.openURL(url) from that click. Show the destination in the UI (the host also names the site in its confirmation) and handle rejection — the user may say no.
3. Without the permission (or on an older Scarf), fall back to copy-to-clipboard and say so: navigator.clipboard.writeText(url) plus a scarf.ui.toast("Link copied"). Never leave a click doing nothing.

async function openLink(url) {
  try { await scarf.openURL(url); }
  catch (e) {                                    // no grant, declined, or too fast
    try { await navigator.clipboard.writeText(url); scarf.ui.toast("Link copied"); }
    catch { scarf.ui.toast(url); }
  }
}

What the host enforces, so you can design for it:

• https only. No http:, no file:, no app schemes, no embedded credentials (https://a.com@b.com is refused), ≤2048 characters.
• The user confirms each new site — "Open example.com in your browser?" with Open Once / Always Allow / Cancel — and "Always" is remembered per project + host. The permission alone opens nothing.
• Only from a real interaction, at human pace. Calls are rate-limited (a handful a minute) and only one confirmation can be on screen: firing openURL on load or in a loop gets you rejections and annoys the user.
• The path and query you put in the URL do travel to that host when the user accepts. Don't smuggle project data into a link.

Hard rules (the sandbox)

1. Self-contained. Assets load over the scarf-miniapp:// scheme scoped to the app dir. Reference local files by relative path (./app.js). No file://, no remote URLs, no external scripts/styles. A link OUT of the app is not an exception to this — it goes through scarf.openURL, which hands the URL to the user's browser rather than loading anything here.
2. Declare every permission you use in miniapp.json.permissions, or the call is denied.
3. Never assume secrets/config/filesystem-at-large. The bridge cannot reach ~/.hermes, config.yaml, auth.json, env, or tools — by design.
4. Degrade gracefully. Check scarf.version if you need a newer bridge; handle empty/permission-denied results without crashing the UI.
5. Keep it small and legible — a single index.html with inline <style>/<script> is ideal for a starter.

Minimal working example — a Kanban task board

Needs only the non-sensitive query:kanban.tasks permission, so it runs immediately as a generated app.

miniapp.json:

{ "id": "task-board", "name": "Task Board", "version": "1.0.0",
  "entry": "index.html", "minBridgeVersion": "1.0",
  "permissions": ["query:kanban.tasks"], "generated": true }

index.html:

<!doctype html>
<html><head><meta charset="utf-8" />
<style>
  body { font: 13px -apple-system, sans-serif; margin: 0; padding: 12px; color: #1d1d1f; }
  h1 { font-size: 15px; margin: 0 0 10px; }
  .task { padding: 8px 10px; border: 1px solid #e3e3e6; border-radius: 8px; margin-bottom: 6px; }
  .status { font-size: 11px; color: #6e6e73; }
  .empty { color: #6e6e73; }
</style></head>
<body>
  <h1 id="title">Tasks</h1>
  <div id="list"><p class="empty">Loading…</p></div>
  <script>
    (async function () {
      document.getElementById("title").textContent = scarf.context.projectName + " — Tasks";
      scarf.ui.setTitle("Task Board");
      const list = document.getElementById("list");
      try {
        const tasks = await scarf.kanban.read();           // [] if none
        if (!tasks.length) { list.innerHTML = '<p class="empty">No tasks yet.</p>'; return; }
        list.innerHTML = "";
        for (const t of tasks) {
          const el = document.createElement("div");
          el.className = "task";
          // textContent (not innerHTML) for task data — titles can come from
          // other users sharing the tenant; never render them as HTML.
          const title = document.createElement("div");
          title.textContent = t.title || "(untitled)";
          const status = document.createElement("div");
          status.className = "status";
          status.textContent = t.status || "";
          el.append(title, status);
          list.appendChild(el);
        }
      } catch (e) {
        list.innerHTML = '<p class="empty">Couldn't load tasks.</p>';
      }
    })();
  </script>
</body></html>

Authoring checklist

1. Pick a short kebab-case <id>; create <project>/.scarf/miniapps/<id>/.
2. Write miniapp.json with id == dir name, "generated": true, and the minimum permissions.
3. Write a self-contained index.html (inline CSS/JS or local files only).
4. Use non-sensitive surfaces first (context, ui, store, query/kanban.read, open_url); request prompt/events/file:read only when needed, and tell the user they'll grant it.
5. If the app shows any external link, declare open_url + "minBridgeVersion": "1.1" and call scarf.openURL from the click — with a copy-to-clipboard fallback. Never ship a bare <a href="https://…">; it does nothing.
6. Tell the user it's ready in the cockpit's Mini-apps panel, and that they'll see a permission preview on first open (sensitive perms start off, for every app).