workflow

CRITICAL: Always Use Correct workflow Documentation

Your knowledge of workflow is outdated.

The workflow documentation outlined below matches the installed version of the Workflow SDK. 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.)
• api-reference/workflow-runtime/ - Runtime API (get-world.mdx) and world/ World SDK (storage.mdx, streams.mdx, queue.mdx)
• api-reference/workflow-observability/ - Hydration and name parsing utilities (hydrate-resource-io.mdx, parse-workflow-name.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 SDK.

Official Resources

• Website: https://workflow-sdk.dev
• GitHub: https://github.com/vercel/workflow

Quick Reference

Directives:

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

Essential imports:

// 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";

// Observability & data hydration
import { hydrateResourceIO, observabilityRevivers, parseStepName, parseWorkflowName } from "workflow/observability";

// 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.

// 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:

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).

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.

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:

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. Deterministic tokens are for createHook() + resumeHook() (server-side) only. createWebhook() always generates random tokens — do not pass a token option to createWebhook().

Single event

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:

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

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:

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 built-in 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, Symbols, WeakMap/WeakSet. Pass data, not callbacks.

Custom Class Serialization

Class instances can be serialized across workflow/step boundaries by implementing the @workflow/serde protocol. This is essential when a class has instance methods with "use step" or when you want to pass class instances between steps.

Install: @workflow/serde must be a dependency of the package containing the class.

Pattern: Add two static methods inside the class bo

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