Workflow DevKit

TypeScript framework for building durable, resumable functions. Workflows survive crashes, deployments, and can pause for days/months.

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

Installation

npm i workflow
# or: pnpm add workflow | yarn add workflow | bun add workflow

Core Concepts

Directives

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

Workflow Function

Orchestrates steps, survives restarts, replays deterministically:

import { sleep } from "workflow";

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

  const user = await createUser(email);      // Step 1
  await sendWelcomeEmail(user);              // Step 2
  await sleep("3 days");                     // Pause (no resources consumed)
  await sendFollowupEmail(user);             // Step 3
  return { userId: user.id };
}

Step Function

Has full Node.js access, auto-retries on failure:

async function createUser(email: string) {
  "use step";
  return await db.users.create({ email });
}

Essential APIs

sleep - Pause Workflow

import { sleep } from "workflow";

await sleep("5s");      // 5 seconds
await sleep("10m");     // 10 minutes
await sleep("1h");      // 1 hour
await sleep("7 days");  // 7 days
await sleep(5000);      // milliseconds
await sleep(new Date("2025-01-01")); // specific date

createHook - Wait for External Input

import { createHook } from "workflow";

const hook = createHook<{ approved: boolean }>();
console.log("Token:", hook.token);  // Send to external system
const result = await hook;          // Pauses until resumed

Resume externally:

import { resumeHook } from "workflow/api";
await resumeHook(token, { approved: true });

createWebhook - HTTP Callback Endpoint

import { createWebhook } from "workflow";

const webhook = createWebhook();
await sendToExternalService(webhook.url);  // Auto-generated URL
const request = await webhook;              // Pauses until HTTP POST
const data = await request.json();

start - Trigger Workflow

import { start } from "workflow/api";

const run = await start(onboardUser, ["user@example.com"]);
console.log(run.runId);  // Returns immediately

Error Handling

import { FatalError, RetryableError } from "workflow";

// Stop retries permanently
throw new FatalError("User not found");

// Retry with delay
throw new RetryableError("Rate limited", { retryAfter: "5m" });

Fetch in Workflows

Workflows run sandboxed. Import fetch from workflow:

import { fetch } from "workflow";

export async function myWorkflow() {
  "use workflow";
  globalThis.fetch = fetch;  // Enable for libraries (AI SDK)

  const response = await fetch("https://api.example.com/data");
}

Streaming (Steps Only)

import { getWritable } from "workflow";

async function streamData(items: string[]) {
  "use step";
  const writer = getWritable();
  for (const item of items) {
    await writer.write({ item });
  }
  writer.releaseLock();
}

Idempotency

Use stepId for external API calls:

import { getStepMetadata } from "workflow";

async function chargeCard(amount: number) {
  "use step";
  const { stepId } = getStepMetadata();
  await stripe.charges.create(
    { amount },
    { idempotencyKey: `charge:${stepId}` }
  );
}

What Cannot Be Serialized

• Functions/callbacks - define logic in steps
• Class instances with methods - use plain objects
• Symbols, WeakMap, WeakSet
• Node.js modules (fs, http, crypto) - use in steps only

Run Status

pending | running | completed | failed | cancelled

References

• Framework Setup: See frameworks.md for Next.js, Express, Hono, Vite, Astro, Fastify, Nitro, Nuxt, SvelteKit
• AI Agents: See ai-agents.md for DurableAgent and streaming patterns
• Advanced Patterns: See patterns.md for hooks, webhooks, control flow
• Common Errors: See errors.md for troubleshooting
• API Reference: See api-reference.md for complete API

Quick Checklist

• Add "use workflow" as first line of workflow function
• Add "use step" as first line of step functions
• Import fetch from workflow and assign to globalThis.fetch
• Use sleep() instead of setTimeout
• Move Node.js module usage to step functions
• Use FatalError for permanent failures, RetryableError for retries
• Configure framework (withWorkflow, nitro module, etc.)