Nitro

This guide will walk through setting up your first workflow in a Nitro v3 project. Along the way, you'll learn more about the concepts that are fundamental to using the Workflow SDK in your own projects.

Create Your Nitro Project

Start by creating a new Nitro v3 project. This command will create a new directory named nitro-app and setup a Nitro project inside it.

npx create-nitro-app

Enter the newly made directory:

cd nitro-app

Install `workflow`

npm i workflow

Configure Nitro

Add workflow/nitro module to your nitro.config.ts This enables usage of the "use workflow" and "use step" directives.

nitro.config.ts

import { defineConfig } from "nitro";

export default defineConfig({
  serverDir: "./server",
  modules: ["workflow/nitro"],
});

Module options

The workflow/nitro module reads its options from workflow on your Nitro config.

nitro.config.ts

import { defineConfig } from "nitro";

export default defineConfig({
  modules: ["workflow/nitro"],
  workflow: {
    runtime: "nodejs22.x",
    sourcemap: "inline",
  },
});

Option	Type	Default	Description
`dirs`	`string[]`	—	Directories to scan for workflows and steps. By default, `workflows/` is scanned from the project root and all layer source directories.
`runtime`	`string`	`'nodejs22.x'`	Node.js runtime version for Vercel Functions (e.g. `'nodejs22.x'`, `'nodejs24.x'`).
`sourcemap`	`boolean \| 'inline' \| 'linked' \| 'external' \| 'both'`	`'inline'`	Controls source maps on generated workflow bundles. Accepts the same values as esbuild's `sourcemap` option. Set to `false` for smaller function bundles (useful for staying under the Vercel 250MB function size limit) at the cost of stack traces pointing at generated code. Can also be set via the `WORKFLOW_SOURCEMAP` environment variable.

Create Your First Workflow

Create a new file for our first workflow:

workflows/user-signup.ts

import { sleep } from "workflow";

export async function handleUserSignup(email: string) {
  "use workflow"; 

  const user = await createUser(email);
  await sendWelcomeEmail(user);

  await sleep("5s"); // Pause for 5s - doesn't consume any resources
  await sendOnboardingEmail(user);

  console.log("Workflow is complete! Run 'npx workflow web' to inspect your run")

  return { userId: user.id, status: "onboarded" };
}

We'll fill in those functions next, but let's take a look at this code:

We define a workflow function with the directive "use workflow". Think of the workflow function as the orchestrator of individual steps.
The Workflow SDK's sleep function allows us to suspend execution of the workflow without using up any resources. A sleep can be a few seconds, hours, days, or even months long.

Create Your Workflow Steps

Let's now define those missing functions.

workflows/user-signup.ts

import { FatalError } from "workflow";

// Our workflow function defined earlier

async function createUser(email: string) {
  "use step"; 

  console.log(`Creating user with email: ${email}`);

  // Full Node.js access - database calls, APIs, etc.
  return { id: crypto.randomUUID(), email };
}

async function sendWelcomeEmail(user: { id: string; email: string }) {
  "use step"; 

  console.log(`Sending welcome email to user: ${user.id}`);

  if (Math.random() < 0.3) {
    // By default, steps will be retried for unhandled errors
    throw new Error("Retryable!");
  }
}

async function sendOnboardingEmail(user: { id: string; email: string }) {
  "use step"; 

  if (!user.email.includes("@")) {
    // To skip retrying, throw a FatalError instead
    throw new FatalError("Invalid Email");
  }

  console.log(`Sending onboarding email to user: ${user.id}`);
}

Taking a look at this code:

Business logic lives inside steps. When a step is invoked inside a workflow, it gets enqueued to run on a separate request while the workflow is suspended, just like sleep.
If a step throws an error, like in sendWelcomeEmail, the step will automatically be retried until it succeeds (or hits the step's max retry count).
Steps can throw a FatalError if an error is intentional and should not be retried.

We'll dive deeper into workflows, steps, and other ways to suspend or handle events in Foundations.

Create Your Route Handler

To invoke your new workflow, we'll create a new API route handler at server/api/signup.post.ts with the following code:

server/api/signup.post.ts

import { start } from "workflow/api";
import { defineEventHandler } from "nitro/h3";
import { handleUserSignup } from "../../workflows/user-signup";

export default defineEventHandler(async ({ req }) => {
  const { email } = await req.json() as { email: string };
  // Executes asynchronously and doesn't block your app
  await start(handleUserSignup, [email]);
  return {
    message: "User signup workflow started",
  }
});

This Route Handler creates a POST request endpoint at /api/signup that will trigger your workflow.

Workflows can be triggered from API routes or any server-side code.

Run in development

To start your development server, run the following command in your terminal in the Nitro root directory:

npm run dev

Once your development server is running, you can trigger your workflow by running this command in the terminal:

curl -X POST --json '{"email":"hello@example.com"}' http://localhost:3000/api/signup

Check the Nitro development server logs to see your workflow execute as well as the steps that are being processed.

Additionally, you can use the Workflow SDK CLI or Web UI to inspect your workflow runs and steps in detail.

# Open the observability Web UI
npx workflow web
# or if you prefer a terminal interface, use the CLI inspect command
npx workflow inspect runs

Workflow SDK Web UI

Deploying to production

Workflow SDK apps currently work best when deployed to Vercel and needs no special configuration.

Enable Fluid compute before deploying. Workflow is designed to take advantage of Fluid compute for efficient suspension and resumption. Without Fluid compute enabled, each workflow resume incurs a separate function cold start, which can result in significantly higher costs.

Check the Deploying section to learn how your workflows can be deployed elsewhere.

Troubleshooting

`start()` says it received an invalid workflow function

If you see this error:

'start' received an invalid workflow function. Ensure the Workflow Development Kit is configured correctly and the function includes a 'use workflow' directive.

Check both of these first:

The workflow function includes "use workflow".
Your Nitro config includes the workflow/nitro module.

See start-invalid-workflow-function for full examples and fixes.

Next Steps

Learn more about the Foundations.
Check Errors if you encounter issues.
Explore the API Reference.

Setup IntelliSense for TypeScript (Optional)

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