extensions

name	extensions
description	Creating, editing, and managing extensions — sandboxed Alpine.js mini-apps that run inside iframes. Use when a user asks for a dashboard, widget, calculator, or any interactive mini-app that calls external APIs. Distinct from LLM "tools" (function calls) — see note below.
metadata	{"internal":true}

Extensions

Terminology note. This skill is about extensions — the framework's user-authored mini-app primitive (sandboxed Alpine.js HTML rendered in an iframe). It is NOT the same thing as LLM "tools", which are the function-calling primitives the AI agent uses (actions, MCP tools, etc.). Other skills still talk about "the agent calls actions as tools" — that's the LLM concept and stays as-is. When this doc says "tool" without qualification, it means LLM tool. When it says "extension", it means the sandboxed mini-app.

Historical naming: extensions were previously called "tools". The physical SQL table names (tools, tool_data, tool_shares) and a few legacy in-iframe globals (toolFetch, toolData) are kept for back-compat — see the back-compat table in references/api.md.

References

• references/api.md — the exhaustive helper/global tables (appAction, appFetch, dbQuery, dbExec, extensionFetch, extensionData), secrets, Tailwind classes, sharing, navigation, routes, and the full back-compat naming table. Read this when you need the precise signature, scope option, or route for any helper.
• references/examples.md — five worked HTML extensions (API status dashboard, weather widget, todo list with extensionData, quick notes). Read this when you want a complete copy-pasteable starting point.

CRITICAL: What Extensions Are (and Are Not)

An Extension is a self-contained Alpine.js HTML snippet stored in the SQL tools table (table name kept for back-compat; the Drizzle export is extensions). It runs inside a sandboxed iframe with its own Tailwind CSS and Alpine.js runtime.

Extensions are NOT:

• React components
• New source code files
• Database schema changes
• Action files in actions/
• Routes

When a user asks to "make an extension", "create an extension", or "build a ... extension" (or the older phrasings "make a tool" / "create a tool"):

1. Write the Alpine.js HTML
2. Call create-extension with the HTML as content
3. That's it — no files to create, no schema changes, no actions

Extensions have full access to app data via helpers injected into the iframe (full signatures in references/api.md):

• appAction(name, params) — call any app action
• appFetch(path, options) — call allowed framework endpoints under /_agent-native/*
• dbQuery(sql, args) — read from SQL
• dbExec(sql, args) — write to SQL
• extensionFetch(url, options) — call external APIs via proxy. Legacy alias: toolFetch — kept for back-compat with extension bodies authored before the rename; both names refer to the same helper.
• extensionData.set/list/get/remove(collection, ...) — persist custom data per-extension (supports { scope: 'user' | 'org' | 'all' } option). Legacy alias: toolData — kept for back-compat; both names refer to the same store.

Data Persistence is Built In

Every extension has extensionData — a per-extension key-value store. NO source code changes, NO Builder, NO new tables needed.

When a user asks to "add persistence", "save data", "remember state", or "store settings" in an extension, use extensionData. It handles table creation, scoping, and upserts automatically. Data is organized into collections per-extension:

// Save a private item (default — only the current user can see it)
await extensionData.set('notes', 'note-1', { title: 'My Note', body: 'Hello' });

// Save an org-shared item (visible to everyone in the org)
await extensionData.set('notes', 'note-1', { title: 'Team Note', body: 'Hello' }, { scope: 'org' });

// List items by scope
const myNotes = await extensionData.list('notes');                        // user-scoped (default)
const orgNotes = await extensionData.list('notes', { scope: 'org' });    // org-scoped only
const allNotes = await extensionData.list('notes', { scope: 'all' });    // both user + org

The legacy global toolData is still injected and points at the same store — older extension bodies that reference toolData.set(...) continue to work without changes. Prefer extensionData in new code.

Prefer extensionData over raw dbExec for extension-specific persistence — it handles everything automatically. Only use dbQuery/dbExec when querying the app's existing tables. See references/api.md for the full get/remove/scope reference.

What extensions are

Extensions are mini Alpine.js apps that run inside sandboxed iframes. They can call external APIs via extensionFetch(), which routes through a server-side proxy that injects secret values. Extensions share the main app's Tailwind v4 theme automatically.

Creating an extension

Call the create-extension action:

pnpm action create-extension \
  --name "GitHub PR Dashboard" \
  --description "Shows open PRs for the repo" \
  --content '<div x-data="...">...</div>'

Or via the HTTP API:

POST /_agent-native/extensions
{ "name": "GitHub PR Dashboard", "description": "Shows open PRs", "content": "<div ...>...</div>" }

The action accepts:

Field	Type	Required	Purpose
name	string	yes	Display name of the extension
description	string	no	Short summary
content	string	yes*	Alpine.js HTML body (*unless contentFromAttachment)
contentFromAttachment	string	no	Host a pasted/attached file verbatim, by reference
icon	string	no	Icon name or short label

See references/examples.md for full, runnable content bodies.

Hosting a pasted file (by reference)

When the user pastes a large file (e.g. a finished HTML/Alpine app) and asks you to host it as an extension, do NOT copy that file into the content argument. A big paste shows up in your context as a <attachment name="pasted-text-…"> block; re-typing it as a tool argument burns thousands of output tokens and frequently gets cut off mid-stream, stalling the turn.

Instead, leave content empty and pass contentFromAttachment set to that attachment's name — or the literal string "latest" for the most recent pasted block. The server reads the attachment verbatim and stores it as the extension content:

{ "name": "My Dashboard", "contentFromAttachment": "latest" }

update-extension accepts the same contentFromAttachment for full-body replacement. Inline content still works for everything you author yourself — use contentFromAttachment only to avoid regurgitating something the user already pasted.

Editing an extension

Use the update-extension action. Prefer granular edits for surgical changes instead of regenerating the full HTML. For medium/large extensions, add stable section comments around major blocks so future agents can target them without touching unrelated indentation:

<!-- agent-native:section npm-daily-chart -->
<section>...</section>
<!-- /agent-native:section npm-daily-chart -->

Then update just that section:

{
  "id": "EXTENSION_ID",
  "edits": "[{\"op\":\"replace-section\",\"section\":\"npm-daily-chart\",\"content\":\"<section>...</section>\"}]",
  "format": true
}

Supported edits operations:

Operation	Use for
replace	Literal find/replace; defaults to one match
insert-before	Insert content before an exact marker
insert-after	Insert content after an exact marker
replace-between	Replace content between two exact markers
replace-section	Replace a named comment section
wrap-section	Add a wrapper around a named section
remove-section	Remove a named section
regex-replace	Carefully scoped regex replacement

Use expectedMatches when ambiguity would be dangerous. Missing required targets fail instead of silently doing nothing. Pass format: true to run Prettier on the final HTML after the patch. Full content replacement is still available for broad rewrites.

Legacy patches still work for simple literal replacements:

PUT /_agent-native/extensions/:id
{
  "patches": [
    { "find": "old HTML fragment", "replace": "new HTML fragment" }
  ]
}

Each patch does a string find-and-replace on the current content. Use this to change a single element, fix a URL, or update a class without rewriting everything.

To replace the full content instead:

PUT /_agent-native/extensions/:id
{ "content": "full new HTML" }

History and rollback

Extensions keep a snapshot history in SQL. A version is recorded when an extension is created, when metadata or HTML content changes, and when a prior version is restored. Existing extensions that predate history get their current state saved as a baseline the first time they are edited.

Use these actions when the user asks what changed, wants a changelog/diff, or wants to go back in time:

Action	Purpose
list-extension-history	List saved versions for one extension
get-extension-history-version	Read one version with a previous-version diff
restore-extension-history-version	Restore name, description, icon, and HTML content from a version

Restoring a version does not restore sharing/ownership; access stays as it is now. In the UI, use the History button in the extension viewer to inspect versions, see diffs, and restore older content.

Alpine.js patterns

Extension HTML uses Alpine.js directives for reactivity. No build step, no imports.

Directive	Purpose	Example
x-data	Reactive state object	x-data="{ count: 0, items: [] }"
x-init	Run on mount (fetch data)	x-init="fetchData()"
x-show	Toggle visibility	x-show="isOpen"
x-if	Conditional render (template)	<template x-if="loaded">...</template>
x-for	Loop	<template x-for="item in items">...</template>
x-text	Set text content	x-text="item.name"
x-html	Set inner HTML	x-html="item.richContent"
x-on:click	Event handler	x-on:click="count++"
x-model	Two-way binding	x-model="searchQuery"
x-bind:class	Dynamic classes	x-bind:class="{ 'font-bold': active }"

Always wrap x-if and x-for in a <template> tag.

Component shape: inline x-data vs. Alpine.data()

For trivial components (a couple of state fields, no methods, no string templating) inline x-data="{ count: 0, items: [] }" is fine. For anything beyond that — multiple methods, string formatting, classification logic, async fetches with branching — put the component in a <script> block and register it with Alpine.data(). The inline form is a string inside an HTML attribute; the longer it gets the more fragile it becomes (one stray quote, one closing-tag-shaped substring, one template literal and the attribute terminates early — Alpine then evaluates a half-parsed expression and throws ReferenceError: <var> is not defined).

Use this pattern for any non-trivial extension:

<div x-data="customerAnalyzer" class="p-4">
  <button @click="analyze()" class="rounded-md bg-primary px-4 py-2 text-sm text-primary-foreground cursor-pointer">
    Analyze
  </button>
  <template x-if="error"><p class="text-red-500" x-text="error"></p></template>
  <template x-if="results">
    <div class="space-y-2">
      <div class="rounded-lg border p-3">
        <p class="font-medium">Action — Builder Side</p>
        <p class="text-sm text-muted-foreground" x-text="results.builderActions.length + ' items'"></p>
      </div>
      <!-- ...other buckets... -->
    </div>
  </template>
</div>

<script>
  document.addEventListener('alpine:init', () => {
    Alpine.data('customerAnalyzer', () => ({
      loading: false,
      error: '',
      results: null,
      async analyze() {
        this.loading = true;
        this.error = '';
        try {
          const { emails } = await appAction('list-emails', { view: 'inbox', limit: 50 });
          // ...categorize into 3 buckets...
          this.results = {
            builderActions: emails.filter((e) => /* ... */),
            waitingOnCustomer: emails.filter((e) => /* ... */),
            fyi: emails.filter((e) => /* ... */),
          };
        } catch (e) {
          this.error = e?.message || 'Analysis failed';
        } finally {
          this.loading = false;
        }
      },
    }));
  });
</script>

Hard rules for x-data / x-* attributes:

• Never put template literals (backticks) inside an HTML attribute. Use string concatenation or pre-format in the script block. Backticks can trip the HTML parser and the resulting string isn't a JS template literal anyway — the attribute is read as plain text.
• Never put a multi-method object literal inline. Move methods into Alpine.data().
• In the <script> block, write normal JS — template literals, async/await, optional chaining all work.
• One source of truth for state: define every variable referenced from any x-text, x-show, x-if, x-for, :class, etc. on the Alpine.data() object's initial state. If x-text="results.foo" references results, results must be a property of the data object — null is a fine initial value as long as you guard with <template x-if="results">.
• When showing an error, render error.message-style text, never a raw boolean. x-text="error" is correct only when error is a string; if it's true the user sees the literal word "true".

AI / LLM features in extensions

Extensions can do AI work two ways. Pick deliberately — silent fallbacks end up rendering nonsense like the literal text true.

1. Delegate to the agent chat. If the user says "analyze my emails", "summarize this", "categorize these tickets" and there is no API key already configured for the relevant provider, prefer doing the work in the agent chat instead of inside the extension. The extension can have a button that calls parent.postMessage({ type: 'agent-native-send-to-chat', message: '...' }), or you can just answer in chat and skip the extension. Don't ship an extension with a stubbed AI step that returns a placeholder — that's how you end up rendering true in red.
2. Call an LLM directly via extensionFetch. Requires a real key the user has set up. Reference it via ${keys.OPENAI_API_KEY} / ${keys.ANTHROPIC_API_KEY} and surface a clear error if the proxy reports the key isn't configured. Tell the user where to add the key (Settings → Secrets) before the extension can work.

If you're not sure a key is configured, ask the user before generating an extension whose primary value is the AI step.

Secrets and sensitive data in extensions

Never put a real API key, token, webhook URL, signing secret, private Builder/internal data, customer data, or credential-looking literal into extension HTML, inline scripts, docs, examples, or extension seed content. Extensions are stored in SQL and rendered in the browser; anything written into the extension body should be treated as visible.

For external API calls, use extensionFetch() with ${keys.NAME} placeholders inside single-quoted strings, for example Authorization: 'Bearer ${keys.GITHUB_TOKEN}'. The proxy resolves the value server-side. If the user has not configured the key, surface a setup error instead of substituting a copied key or demo value.

Guidelines

• Rely on the default canvas padding. The iframe shell adds modest body padding so simple extensions do not hug the edge. Do not add outer p-4 / p-6 unless the design needs extra breathing room. For full-bleed extensions such as maps, canvases, or custom editors, put data-tool-layout="full-bleed" or data-tool-padding="none" on the outermost element. (The data-tool-* attribute names are kept for back-compat with the iframe runtime.)
• Use semantic Tailwind colors for native theming. Always use bg-background, text-foreground, bg-primary, text-primary-foreground, border-border, bg-muted, text-muted-foreground, etc. The extension inherits the parent app's exact theme variables, so it will look fully native in both light and dark modes.
• Keep extensions focused. One extension, one job. A "GitHub PR Dashboard" should show PRs, not also manage issues.
• Handle loading and error states. Always show a loading indicator during fetch and handle failures gracefully.
• All functions referenced in Alpine expressions must be defined in x-data. If you use @click="add()", there must be an add() method in the component's x-data object. Undefined references cause runtime errors.
• For non-trivial components, use a <script> + Alpine.data('name', () => ({...})) block and reference it with x-data="name". Inline x-data="{ ...big object... }" is brittle: stuffing many methods, branching logic, or any backtick template literal into an HTML attribute leads to half-parsed expressions and ReferenceError failures. See the "Component shape" section above.
• Don't ship a stubbed AI step. If the extension's value is "AI analysis" and no LLM key is configured, either route the work to the agent chat or tell the user which key to add — never render a placeholder/boolean as the result.
• Never hardcode secrets or private data. Use ${keys.NAME} placeholders for external credentials and synthetic example data for demos.
• Use the right fetch helper. appAction() for app actions and app data, appFetch() for allowed framework /_agent-native/* endpoints, and extensionFetch() for external APIs. Never call template /api/* routes from an extension and never use raw fetch() -- secrets won't be injected and CORS will block external APIs.
• Single quotes around ${keys.*} to prevent browser-side template literal evaluation.
• Prefer patches over full rewrites when editing existing extensions. Smaller diffs are less error-prone.

Related skills

• extension-points -- how an extension renders as a widget inside another app via named UI slots.
• secrets -- creating and managing API keys for ${keys.NAME} substitution.
• sharing -- visibility and access control for extensions.
• actions -- the create-extension, update-extension, and extension history actions that back extension CRUD and rollback.
• frontend-design -- design guidance when styling extension HTML.