vercel / workflow

Skill Content

---
name: workflow
description: Creates durable, resumable workflows using Vercel's Workflow DevKit. Use when building workflows that need to survive restarts, pause for external events, retry on failure, or coordinate multi-step operations over time. Triggers on mentions of "workflow", "durable functions", "resumable", "workflow devkit", or step-based orchestration.
metadata:
  author: Vercel Inc.
  version: '1.1'
---

## *CRITICAL*: Always Use Correct `workflow` Documentation

Your knowledge of `workflow` is outdated.

The `workflow` documentation outlined below matches the installed version of the Workflow DevKit.
Follow these instructions before starting on any `workflow`-related tasks:

Search the bundled documentation in `node_modules/workflow/docs/`:

1. **Find docs**: `glob "node_modules/workflow/docs/**/*.mdx"`
2. **Search content**: `grep "your query" node_modules/workflow/docs/`

Documentation structure in `node_modules/workflow/docs/`:

- `getting-started/` - Framework setup (next.mdx, express.mdx, hono.mdx, etc.)
- `foundations/` - Core concepts (workflows-and-steps.mdx, hooks.mdx, streaming.mdx, etc.)
- `api-reference/workflow/` - API docs (sleep.mdx, create-hook.mdx, fatal-error.mdx, etc.)
- `api-reference/workflow-api/` - Client API (start.mdx, get-run.mdx, resume-hook.mdx, etc.)
- `ai/` - AI SDK integration docs
- `errors/` - Error code documentation

Related packages also include bundled docs:

- `@workflow/ai`: `node_modules/@workflow/ai/docs/` - DurableAgent and AI integration
- `@workflow/core`: `node_modules/@workflow/core/docs/` - Core runtime (foundations, how-it-works)
- `@workflow/next`: `node_modules/@workflow/next/docs/` - Next.js integration

**When in doubt, update to the latest version of the Workflow DevKit.**

### Official Resources

- **Website**: https://useworkflow.dev
- **GitHub**: https://github.com/vercel/workflow

### Quick Reference

**Directives:**

```typescript
"use workflow";  // First line - makes async function durable
"use step";      // First line - makes function a cached, retryable unit
```

**Essential imports:**

```typescript
// Workflow primitives
import { sleep, fetch, createHook, createWebhook, getWritable } from "workflow";
import { FatalError, RetryableError } from "workflow";
import { getWorkflowMetadata, getStepMetadata } from "workflow";

// API operations
import { start, getRun, resumeHook, resumeWebhook } from "workflow/api";

// Framework integrations
import { withWorkflow } from "workflow/next";
import { workflow } from "workflow/vite";
import { workflow } from "workflow/astro";
// Or use modules: ["workflow/nitro"] for Nitro/Nuxt

// AI agent
import { DurableAgent } from "@workflow/ai/agent";
```

## Prefer Step Functions to Avoid Sandbox Errors

`"use workflow"` functions run in a sandboxed VM. `"use step"` functions have **full Node.js access**. Put your logic in steps and use the workflow function purely for orchestration.

```typescript
// Steps have full Node.js and npm access
async function fetchUserData(userId: string) {
  "use step";
  const response = await fetch(`https://api.example.com/users/${userId}`);
  return response.json();
}

async function processWithAI(data: any) {
  "use step";
  // AI SDK works in steps without workarounds
  return await generateText({
    model: openai("gpt-4"),
    prompt: `Process: ${JSON.stringify(data)}`,
  });
}

// Workflow orchestrates steps - no sandbox issues
export async function dataProcessingWorkflow(userId: string) {
  "use workflow";
  const data = await fetchUserData(userId);
  const processed = await processWithAI(data);
  return { success: true, processed };
}
```

**Benefits:** Steps have automatic retry, results are persisted for replay, and no sandbox restrictions.

## Workflow Sandbox Limitations

When you need logic directly in a workflow function (not in a step), these restrictions apply:

| Limitation | Workaround |
|------------|------------|
| No `fetch()` | `import { fetch } from "workflow"` then `globalThis.fetch = fetch` |
| No `setTimeout`/`setInterval` | Use `sleep("5s")` from `"workflow"` |
| No Node.js modules (fs, crypto, etc.) | Move to a step function |

**Example - Using fetch in workflow context:**

```typescript
import { fetch } from "workflow";

export async function myWorkflow() {
  "use workflow";
  globalThis.fetch = fetch;  // Required for AI SDK and HTTP libraries
  // Now generateText() and other libraries work
}
```

**Note:** `DurableAgent` from `@workflow/ai` handles the fetch assignment automatically.

## DurableAgent — AI Agents in Workflows

Use `DurableAgent` to build AI agents that maintain state and survive interruptions. It handles the workflow sandbox automatically (no manual `globalThis.fetch` needed).

```typescript
import { DurableAgent } from "@workflow/ai/agent";
import { getWritable } from "workflow";
import { z } from "zod";
import type { UIMessageChunk } from "ai";

async function lookupData({ query }: { query: string }) {
  "use step";
  // Step functions have full Node.js access
  return `Results for "${query}"`;
}

export async function myAgentWorkflow(userMessage: string) {
  "use workflow";

  const agent = new DurableAgent({
    model: "anthropic/claude-sonnet-4-5",
    system: "You are a helpful assistant.",
    tools: {
      lookupData: {
        description: "Search for information",
        inputSchema: z.object({ query: z.string() }),
        execute: lookupData,
      },
    },
  });

  const result = await agent.stream({
    messages: [{ role: "user", content: userMessage }],
    writable: getWritable<UIMessageChunk>(),
    maxSteps: 10,
  });

  return result.messages;
}
```

**Key points:**
- `getWritable<UIMessageChunk>()` streams output to the workflow run's default stream
- Tool `execute` functions that need Node.js/npm access should use `"use step"`
- Tool `execute` functions that use workflow primitives (`sleep()`, `createHook()`) should **NOT** use `"use step"` — they run at the workflow level
- `maxSteps` limits the number of LLM calls (default is unlimited)
- Multi-turn: pass `result.messages` plus new user messages to subsequent `agent.stream()` calls

**For more details on `DurableAgent`, check the AI docs in `node_modules/@workflow/ai/docs/`.**

## Starting Workflows & Child Workflows

Use `start()` to launch workflows from API routes. **`start()` cannot be called directly in workflow context** — wrap it in a step function.

```typescript
import { start } from "workflow/api";

// From an API route — works directly
export async function POST() {
  const run = await start(myWorkflow, [arg1, arg2]);
  return Response.json({ runId: run.runId });
}

// No-args workflow
const run = await start(noArgWorkflow);
```

**Starting child workflows from inside a workflow — must use a step:**

```typescript
import { start } from "workflow/api";

// Wrap start() in a step function
async function triggerChild(data: string) {
  "use step";
  const run = await start(childWorkflow, [data]);
  return run.runId;
}

export async function parentWorkflow() {
  "use workflow";
  const childRunId = await triggerChild("some data");  // Fire-and-forget via step
  await sleep("1h");
}
```

`start()` returns immediately — it doesn't wait for the workflow to complete. Use `run.returnValue` to await completion.

## Hooks — Pause & Resume with External Events

Hooks let workflows wait for external data. Use `createHook()` inside a workflow and `resumeHook()` from API routes.

### Single event

```typescript
import { createHook } from "workflow";

export async function approvalWorkflow() {
  "use workflow";

  const hook = createHook<{ approved: boolean }>({
    token: "approval-123",  // deterministic token for external systems
  });

  const result = await hook;  // Workflow suspends here
  return result.approved;
}
```

### Multiple events (iterable hooks)

Hooks implement `AsyncIterable` — use `for await...of` to receive multiple events:

```typescript
import { createHook } from "workflow";

export async function chatWorkflow(channelId: string) {
  "use workflow";

  const hook = createHook<{ text: string; done?: boolean }>({
    token: `chat-${channelId}`,
  });

  for await (const event of hook) {
    await processMessage(event.text);
    if (event.done) break;
  }
}
```

Each `resumeHook(token, payload)` call delivers the next value to the loop.

### Resuming from API routes

```typescript
import { resumeHook } from "workflow/api";

export async function POST(req: Request) {
  const { token, data } = await req.json();
  await resumeHook(token, data);
  return new Response("ok");
}
```

## Error Handling

Use `FatalError` for permanent failures (no retry), `RetryableError` for transient failures:

```typescript
import { FatalError, RetryableError } from "workflow";

if (res.status >= 400 && res.status < 500) {
  throw new FatalError(`Client error: ${res.status}`);
}
if (res.status === 429) {
  throw new RetryableError("Rate limited", { retryAfter: "5m" });
}
```

## Serialization

All data passed to/from workflows and steps must be serializable.

**Supported types:** string, number, boolean, null, undefined, bigint, plain objects, arrays, Date, RegExp, URL, URLSearchParams, Map, Set, Headers, ArrayBuffer, typed arrays, Request, Response, ReadableStream, WritableStream.

**Not supported:** Functions, class instances, Symbols, WeakMap/WeakSet. Pass data, not callbacks.

## Streaming

Use `getWritable()` to stream data from workflows. `getWritable()` can be called in **both** workflow and step contexts, but you **cannot interact with the stream** (call `getWriter()`, `write()`, `close()`) directly in a workflow function. The stream must be passed to step functions for actual I/O, or steps can call `getWritable()` themselves.

**Get the stream in a workflow, pass it to a step:**
```typescript
import { getWritable } from "workflow";

export async function myWorkflow() {
  "use workflow";
  const writable = getWritable();
  await writeData(writable, "hello world");
}

async function writeData(writable: WritableStream, chunk: string) {
  "use step";
  const writer = writable.getWriter();
  try {
    await writer.write(chunk);
  } finally {
    writer.releaseLock();
  }
}
```

**Call `getWritable()` directly inside a step (no need to pass it):**
```typescript
import { getWritable } from "workflow";

async function streamData(chunk: string) {
  "use step";
  const writer = getWritable().getWriter();
  try {
    await writer.write(chunk);
  } finally {
    writer.releaseLock();
  }
}
```

## Debugging

```bash
# Check workflow endpoints are reachable
npx workflow health
npx workflow health --port 3001  # Non-default port

# Visual dashboard for runs
npx workflow web
npx workflow web <run_id>

# CLI inspection (use --json for machine-readable output, --help for full usage)
npx workflow inspect runs
npx workflow inspect run <run_id>

# For Vercel-deployed projects, specify backend and project
npx workflow inspect runs --backend vercel --project <project-name> --team <team-slug>
npx workflow inspect run <run_id> --backend vercel --project <project-name> --team <team-slug>

# Open Vercel dashboard in browser for a specific run
npx workflow inspect run <run_id> --web
npx workflow web <run_id> --backend vercel --project <project-name> --team <team-slug>

# Cancel a running workflow
npx workflow cancel <run_id>
npx workflow cancel <run_id> --backend vercel --project <project-name> --team <team-slug>
# --env defaults to "production"; use --env preview for preview deployments
```

**Debugging tips:**
- Use `--json` (`-j`) on any command for machine-readable output
- Use `--web` to open the Vercel Observability dashboard in your browser
- Use `--help` on any command for full usage details
- Only import workflow APIs you actually use. Unused imports can cause 500 errors.