Unified Apps

A Unified App is a reusable action that runs on Fused. It combines your logic with calls to one or more services, giving your product or agent one action to call. For example, an onboard customer action could create a customer in your CRM, send a welcome email, and return the new customer’s ID. Use it to keep a workflow in one place and reuse it across your products and agents. You define its inputs, steps, and result in TypeScript. Fused hosts the action and supplies credentials for the service operations you allow it to use.

Create your first app

Start with a configured CLI and your service credentials in the default bucket. You need access to create apps and use that bucket.

Start with a prompt or code

To have Fused draft the files, run this in an interactive terminal:

fused-cli describe --name customer-app --bucket default \
  "Use my CRM to create a customer. Accept name and email as strings. Return customerId as a string."

Fused finds the service and operation, then drafts the TypeScript and YAML for you. Review its proposal and confirm to deploy.To write the app yourself, save these two files as customer-app.ts and customer-app.yaml in .fused/unified_app/:

import * as z from "zod/mini";
import { buildUnifiedApp } from "@fused/unified-app";
import { services } from "@fused/operations";

export default buildUnifiedApp({
  input: z.object({ name: z.string(), email: z.string() }),
  output: z.object({ customerId: z.string() }),
  // Expose one customer-creation action through the selected provider operation.
  async execute({ input }) {
    const customer = await services["@your-provider/crm"].createCustomer({
      name: input.name,
      email: input.email,
    });
    return { customerId: customer.id };
  },
});

apiVersion: fused/v1
kind: unified_app
name: customer-app
version: "1.0.0"
bucket: default
source_path: customer-app.ts
services:
  "@your-provider/crm":
    version: "2026-01-01"
    operations: [createCustomer]

This example assumes a CRM operation that accepts name and email and returns id. Replace @your-provider/crm, the service version, and operation with the exact values in your workspace. Use the same service reference in both files.

Deploy your files

If you wrote the files yourself, review the plan and apply it:

fused-cli app plan -f .fused/unified_app/customer-app.yaml
fused-cli app apply -f .fused/unified_app/customer-app.yaml

If you already confirmed deployment through describe, continue to the call below.Save the returned app family ID (app_family_id) and execution token. The token is shown once. Deployment does not create a customer; calling the app does.

Call your app

Set FUSED_ENGINE_URL to your Engine’s HTTP address. Use the app family ID and execution token from deployment for FUSED_APP_FAMILY_ID and FUSED_APP_TOKEN.

curl -X POST "$FUSED_ENGINE_URL/v1/apps/$FUSED_APP_FAMILY_ID/executions" \
  -H "Authorization: Bearer $FUSED_APP_TOKEN" \
  -H 'Content-Type: application/json' \
  -d '{"operation":"execute","input":{"name":"Jane","email":"jane@example.com"}}'

A successful response includes:

{
  "status": "succeeded",
  "output": { "customerId": "cus_123" }
}

output is what your function returns. If the response is still queued or running, retrieve the result.

Keep building

Write the code yourself

Create the two files: TypeScript for the action and YAML for its selected operations.

Update or roll back

Deploy a change or switch traffic to a previous version.

Call from an SDK or MCP

Reuse the same action in another app or agent.

Read results and debug

Retrieve pending results and inspect failed requests.

Get Started

Guides

Advanced

Reference

Unified Apps

Create your first app

Keep building

Write the code yourself

Update or roll back

Call from an SDK or MCP

Read results and debug

​Create your first app

​Keep building

Write the code yourself

Update or roll back

Call from an SDK or MCP

Read results and debug

Create your first app

Keep building