---
title: Author an app
description: "Write an app in plain TypeScript: a provider, some queries and mutations, the approvals that guard them, stored data, and the call that deploys it."
---

An app is TypeScript source with a default `defineApp` export from the `apps`
package. One `index.ts` is enough to use the framework supplied by the host.
To author outside the monorepo and select a framework version, install the
Executor beta of `apps` and deploy your `package.json` with the source:

```sh
npm install --save-exact apps@0.0.1-beta.0
```

The first beta is being prepared. Until it is published, use a locally packed
tarball. Do not install `apps@latest`: that tag is separate from this beta series.

When `dependencies.apps` is present, Executor uses that package's server and
browser framework. It retains the compiled code with the deployment, so host
updates do not replace it. An exact version also keeps rebuilds on that version;
a version range or tag can select a newer version on the next build.
An unavailable or unsupported package fails the build and leaves the active app
unchanged. The host protocol is small and shared; early beta releases do not
promise indefinite support for every past version.

`defineApp` declares behavior and does not take a name. Set the package name
in `package.json`, such as `"name": "@team/calendar"` when publishing. The name
you choose when creating or renaming an installed app is its editable display label.

Write ordinary async TypeScript. You do not import Effect and you do not import
the Executor SDK. The framework validates input and supplies the selected
accounts.

## A first app

```ts
import { query, defineApp, object, string } from "apps";

const Greet = object({ name: string().default("world") });

export default defineApp(
  { accounts: {} },
  {
    queries: {
      greet: query(
        { description: "Greet someone by name", input: Greet },
        async (_ctx, { name }) => ({ message: `Hello, ${name}!` }),
      ),
    },
  },
);
```

`defineApp(requirements, definition)` takes what the app needs and what it
offers. `query(options, handler)` and `mutation(options, handler)` declare the
operations. Options are `description`, `input`, and optionally `output` and
`approval`.

The schema helpers are `object`, `string`, `number`, `boolean`, `array`,
`record`, `json` and `literal`. Use `.optional()` for a field that may be absent
and `.default(value)` for a default. `object` strips properties you did not
declare. `Infer<typeof Input>` gives you the parsed input type.

## Using an account

Declare a provider, require it, and read it off the context.

```ts
import {
  query,
  type QueryContext,
  array,
  decodeJson,
  defineApp,
  defineProvider,
  object,
  secrets,
  string,
} from "apps";

const vercel = defineProvider({
  name: "Vercel",
  auth: {
    apiKey: secrets({
      label: "API token",
      fields: object({ token: string({ minLength: 1 }) }),
    }),
  },
});

const requirements = { accounts: { vercel } };
type Context = QueryContext<typeof requirements>;

const Projects = object({ projects: array(object({ id: string(), name: string() })) });

const listProjects = query(
  { description: "List projects for the selected Vercel account", input: object({}) },
  async ({ accounts, fetch }: Context) => {
    const response = await fetch("https://api.vercel.com/v9/projects?limit=10", {
      headers: { Authorization: `Bearer ${accounts.vercel.fields.token}` },
    });
    return decodeJson(response, Projects);
  },
);

export default defineApp(requirements, { queries: { listProjects } });
```

`accounts.vercel.fields` holds exactly the fields the method declared. The token
arrives per call, from whichever account the app has selected. Nothing in the
source names an account, so the same code serves a work app and a personal one.

`decodeJson(response, schema)` checks the HTTP status and parses the body. Use
`oauth2({ discover: "..." })` instead of `secrets` for a browser sign-in; the
access token then arrives as `accounts.<slot>.fields.access_token`.

For a slot that takes several accounts, use `provider.many()`. The context gives
you a list.

## Queries and mutations

Both become tools. The difference is what they may do to the app's own stored
data.

- A query gets a read-only view.
- A mutation writes in a transaction that commits only after its output
  validates.

External calls are allowed from both, and external effects are never rolled
back.

## Approvals

Approval is declared on the operation.

```ts
import { always, never } from "apps/operations/approval";

// in the operation options:
approval: always(),   // ask a person first
approval: never(),    // run without asking
```

A function gets the real decision. It receives the tool name, the decoded input
and an abort signal, and returns `approved`, `denied` or `user-approval`.
Annotate a shared one with `Approval<Input>` to reuse it. For an imported
operation, wrap it: `withApproval(operation, policy)`.

There is no app-level approval setting, and nothing is inferred from an
operation looking read-only. See
[Tools and approvals](/concepts/tools-and-approvals).

## Asking for input mid-tool

```ts
await ctx.elicit({
  mode: "form",
  message: "Name this result",
  requestedSchema: {
    type: "object",
    properties: { name: { type: "string" } },
    required: ["name"],
  },
});
```

The question reaches the person the same way an approval does.

## Importing an existing service

You do not have to write handlers to wrap an API.

```ts
import { defineApp } from "apps";
import { mcpOperations } from "apps/mcp";

export default defineApp({ accounts: {} }, async ({ signal }) => ({
  ...(await mcpOperations({
    url: "https://mcp.deepwiki.com/mcp",
    ...(signal === undefined ? {} : { signal }),
  })),
}));
```

The helpers are `mcpOperations` from `apps/mcp`, `stdioOperations` from
`apps/mcp/stdio`, `graphqlOperations` from `apps/graphql` and
`openapiOperations` from `apps/openapi`. Each returns `{ queries, mutations }`.
An operation that cannot be classified becomes a mutation.

The dashboard's **Custom app** form does the same thing from a URL, for MCP,
GraphQL and OpenAPI, without writing any source.

## Storing data

Declare a database and the app gets tables.

```ts
import { defineDatabase, object, string, table } from "apps";

const database = defineDatabase({
  messages: table({ mailbox: string(), subject: string() }).index("by_mailbox", ["mailbox"]),
});

const requirements = { accounts: {}, database };
```

Query it through `db` on the context, with `withIndex`, `order`, and a terminal:
`first`, `take`, `collect`, `count` or `paginate({ cursor, numItems })`. A
`by_creation` index exists without being declared.

Reads are bounded: 5,000 rows scanned, 1,000 returned, 4 MiB per invocation.
`collect` and `count` fail rather than truncate, so you notice. A mutation
allows 1,000 writes.

## Shipping instructions

An app can carry its own guidance for agents. Put it beside the source:

<FileTree>

- index.ts
- skills/
  - triage/
    - SKILL.md
    - references/
      - examples.md

</FileTree>

```md
---
name: triage
description: Search cached messages before fetching more history.
---

Read [examples](references/examples.md), then discover this app's queries.
```

An agent reads it with the `skills` tool. Skill text never grants a permission;
the approval still decides.

## Deploying

Deployment is an operation, not a command. Have your agent call it through the
MCP endpoint.

<CodeGroup>

```js Hosted
return await tools.executor.mutations.apps_deploy({
  path: { organization: "<approved-organization-id>" },
  body: {
    name: "Hello",
    files: [{ path: "index.ts", content: "<contents of index.ts>" }],
  },
});
```

```js Local
return await tools.executor.mutations.apps_deploy({
  body: {
    owner: "my-project",
    name: "Hello",
    files: [{ path: "index.ts", content: "<contents of index.ts>" }],
  },
});
```

</CodeGroup>

The app activates only after the build succeeds, and earlier deployments are
retained; see [Apps and deployments](/concepts/apps-and-deployments). Then
connect an account for each requirement and call it in a new `execute`:

```js
return await tools["<app-slug>"].queries.greet({ name: "Ada" });
```

### Updating an existing app

Create-by-name calls reject an existing name. Edit an existing app through the
same source, commit and deploy operations on Local and Hosted. Read their current
signatures first. Hosted paths include `organization`; Local paths contain only
`app`.

```js
const api = tools.executor;
const path = { organization: "<approved-organization-id>", app: "<app-id>" };
const app = await api.queries.apps_get({ path });
const source = await api.queries.appManagement_source({ path });
const saved = await api.mutations.appManagement_commit({
  path,
  body: {
    expected: source.revision.commit,
    message: "Update greeting",
    files: [{ path: "index.ts", content: "<complete updated source>" }],
  },
});
return await api.mutations.appManagement_deploy({
  path,
  body: { expectedSource: saved.revision.commit, expectedDeployment: app.activeDeployment },
});
```

The commit replaces the complete file list. Saving source does not deploy it.
Web pages show source; agents or ordinary Git clients edit it.

Discovery is not cached across a change, so run `tools.search` again after you
deploy.

The CLI also provides `executor apps source`, `executor apps commit`, and
`executor apps deploy`. Deploy the chosen commit with its expected running
version. Ordinary Git pushes save source without deploying it.

## Update a hosted app

Read the current source with `apps_source`. Submit the complete edited file set
through `apps_update`, with `expectedDeployment` set to the source response's
`id`. The app keeps its ID and stored data. If another deployment won the race,
read the source again before retrying. Use `apps_activate` to select a retained
deployment; activation does not roll back stored data.

## Open an app UI

React is the only supported app UI framework for now. Include `ui/index.html`,
a React entry such as `ui/main.tsx`, and styles in the deployment. Declare
`react` and `react-dom` in the app's package dependencies. The host builds and
activates the browser assets with the server code. No separate publish step is
needed. SSR and React Server Components are not supported yet.

You can bring your own React components or browser-compatible npm component
libraries. Declare their dependencies and include the required styles and
assets. Libraries that need custom build plugins require additional build
support.

Tailwind CSS v4 compilation is built in. Import a stylesheet from your React
entry:

```tsx
import "./style.css";
```

Start `ui/style.css` with:

```css
@import "tailwindcss";
```

Write complete utility classes in your React components. No Tailwind dependency,
config file or separate build command is needed. The build scans browser code,
including imported components and lazy chunks. Ordinary CSS and component-library
styles can share the same app.

Use CSS `@theme` for custom tokens. Use `@source inline("...")` to include classes
that only arrive at runtime. Filesystem `@source` paths and JavaScript `@config`
or `@plugin` files are not supported.

For hosted apps, discover `appUi_location` through `tools.search` and call it:

```js
return await tools.executor.queries.appUi_location({
  path: { organization: "<approved-organization-id>", app: "<app-id>" },
});
```

Open the returned `url` in a browser. Executor Cloud uses
`https://<app-slug>.<org-slug>.executor.website`; self-host uses its configured
app domain. Use the returned URL instead of guessing it. A null URL means the
app has no UI or the host has no app domain configured.

App pages are private. Opening the link starts browser sign-in through Executor.
A successful tool call or a `403` from a guessed address does not verify that
the UI renders. Check the actual page before reporting it as working.

## What is coming later

- Scheduled and background work.
- Calling one app from another.
- Authoring general HTTP endpoints.
- Stored-data schema migration between deployments.
- A local `executor dev` loop.