---
title: Fastify
description: Set up your first durable workflow in a Fastify application.
type: guide
summary: Set up Workflow SDK in a Fastify app.
prerequisites:
  - /docs/getting-started
related:
  - /docs/foundations/workflows-and-steps
---

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

---

<Steps>

<Step>
## Create Your Fastify Project

Start by creating a new Fastify project.

```bash
mkdir my-workflow-app
```

Enter the newly made directory:

```bash
cd my-workflow-app
```

Initialize the project:

```bash
npm init --y
```

### Install `workflow`, `fastify` and `nitro`

```package-install
npm i workflow fastify nitro rollup
```

<Callout>
By default, Fastify doesn't include a build system. Nitro adds one which enables compiling workflows, runs, and deploys for development and production. Learn more about [Nitro](https://v3.nitro.build).
</Callout>

If using TypeScript, you need to install the `@types/node` and `typescript` packages

```bash
npm i -D @types/node typescript
```

### Configure Nitro

Create a new file `nitro.config.ts` for your Nitro configuration with module `workflow/nitro`. This enables usage of the `"use workflow"` and `"use step"` directives

```typescript title="nitro.config.ts" lineNumbers
import { defineNitroConfig } from "nitro/config";

export default defineNitroConfig({
	modules: ["workflow/nitro"],
	vercel: { entryFormat: "node" },
	routes: {
		"/**": { handler: "./src/index.ts", format: "node" },
	},
});
```

<Accordion type="single" collapsible>
  <AccordionItem value="typescript-intellisense" className="[&_h3]:my-0">
    <AccordionTrigger className="[&_p]:my-0 text-lg [&_p]:text-foreground">
      Setup IntelliSense for TypeScript (Optional)
    </AccordionTrigger>
    <AccordionContent className="[&_p]:my-2">
To enable helpful hints in your IDE, set up the workflow plugin in `tsconfig.json`:

```json title="tsconfig.json" lineNumbers
{
  "compilerOptions": {
    // ... rest of your TypeScript config
    "plugins": [
      {
        "name": "workflow" // [!code highlight]
      }
    ]
  }
}
```

    </AccordionContent>
  </AccordionItem>
</Accordion>

### Update `package.json`

To use the Nitro builder, update your `package.json` to include the following scripts:

```json title="package.json" lineNumbers
{
  // ...
  "scripts": {
    "dev": "nitro dev",
    "build": "nitro build"
  },
  // ...
}
```

</Step>

<Step>

## Create Your First Workflow

Create a new file for our first workflow:

```typescript title="workflows/user-signup.ts" lineNumbers
import { sleep } from "workflow";

export async function handleUserSignup(email: string) {
  "use workflow"; // [!code highlight]

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

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

  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:
```typescript title="workflows/user-signup.ts" lineNumbers
import { FatalError } from "workflow";

// Our workflow function defined earlier

async function createUser(email: string) {
  "use step"; // [!code highlight]
  console.log(`Creating user with email: ${email}`);
  return { id: crypto.randomUUID(), email };
}

async function sendWelcomeEmail(user: { id: string; email: string }) {
  "use step"; // [!code highlight]
  console.log(`Sending welcome email to user: ${user.id}`);
  if (Math.random() < 0.3) {
    // Steps retry on unhandled errors
    throw new Error("Retryable!");
  }
}

async function sendOnboardingEmail(user: { id: string; email: string }) {
  "use step"; // [!code highlight]
  if (!user.email.includes("@")) {
    // FatalError skips retries
    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.

<Callout>
  We'll dive deeper into workflows, steps, and other ways to suspend or handle
  events in [Foundations](/docs/foundations).
</Callout>
</Step>

<Step>

## Create Your Route Handler

To invoke your new workflow, we'll create both the Fastify app and a new API route handler at `src/index.ts` with the following code:

```typescript title="src/index.ts"
import Fastify from "fastify";
import { start } from "workflow/api";
import { handleUserSignup } from "../workflows/user-signup.js";

const app = Fastify({ logger: true });
app.post("/api/signup", async (req, reply) => {
  const { email } = req.body as { email: string };
  await start(handleUserSignup, [email]);
  return reply.send({ message: "User signup workflow started" });
});

// Wait for Fastify to be ready before handling requests
await app.ready();


export default (req: any, res: any) => {
  app.server.emit("request", req, res);
};
```
This route handler creates a `POST` request endpoint at `/api/signup` that will trigger your workflow.
</Step>

<Step>

## Run in development

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

```bash
npm run dev
```

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

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

Check the Fastify 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](/docs/observability) to inspect your workflow runs and steps in detail.

```bash
npx workflow inspect runs # add '--web' for an interactive Web based UI
```

![Workflow SDK Web UI](/o11y-ui.png)

</Step>

</Steps>

---

## Deploying to production

Workflow SDK apps currently work best when deployed to [Vercel](https://vercel.com/home) and needs no special configuration.

<FluidComputeCallout />

Check the [Deploying](/docs/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:

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

See [start-invalid-workflow-function](/docs/errors/start-invalid-workflow-function) for full examples and fixes.

## Next Steps

- Learn more about the [Foundations](/docs/foundations).
- Check [Errors](/docs/errors) if you encounter issues.
- Explore the [API Reference](/docs/api-reference).