Vercel Workflow SDK expert guidance. Use when building durable workflows, long-running tasks, API routes or agents that need pause/resume, retries, step-based execution, or crash-safe orchestration with Vercel Workflow.
Scanned 9/2/2026
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---
name: workflow
description: Vercel Workflow SDK expert guidance. Use when building durable workflows, long-running tasks, API routes or agents that need pause/resume, retries, step-based execution, or crash-safe orchestration with Vercel Workflow.
metadata:
priority: 9
docs:
- "https://vercel.com/docs/workflow"
- "https://workflow-sdk.dev"
sitemap: "https://vercel.com/sitemap.xml"
pathPatterns:
- 'lib/workflow/**'
- 'src/lib/workflow/**'
- 'lib/workflow.*'
- 'src/lib/workflow.*'
- 'workflow.*'
- '*workflow*'
importPatterns:
- '@vercel/workflow'
- 'workflow'
- '@workflow/*'
- '*workflow*'
bashPatterns:
- '\bnpm\s+(install|i|add)\s+[^\n]*@vercel/workflow\b'
- '\bpnpm\s+(install|i|add)\s+[^\n]*@vercel/workflow\b'
- '\bbun\s+(install|i|add)\s+[^\n]*@vercel/workflow\b'
- '\byarn\s+add\s+[^\n]*@vercel/workflow\b'
- '\bnpm\s+(install|i|add)\s+[^\n]*\bworkflow\b'
- '\bpnpm\s+(install|i|add)\s+[^\n]*\bworkflow\b'
- '\bbun\s+(install|i|add)\s+[^\n]*\bworkflow\b'
- '\byarn\s+add\s+[^\n]*\bworkflow\b'
- '\bnpm\s+(install|i|add)\s+[^\n]*@workflow/'
- '\bpnpm\s+(install|i|add)\s+[^\n]*@workflow/'
- '\bbun\s+(install|i|add)\s+[^\n]*@workflow/'
- '\byarn\s+add\s+[^\n]*@workflow/'
- '\bnpx\s+workflow(?:@latest)?\b'
- '\bbunx\s+workflow(?:@latest)?\b'
promptSignals:
phrases:
# Direct workflow mentions
- "vercel workflow"
- "workflow sdk"
# Legacy product name retained only as an input matcher.
- "workflow devkit"
- "durable workflow"
- "durable execution"
- "durable function"
- "durable pipeline"
- "durable process"
- "durable agent"
- "durable chat"
- "step function"
- "step functions"
- "use workflow"
- "use step"
# Pipeline / multi-step language (the BIG gap — natural product prompts)
- "multi-step pipeline"
- "multi step pipeline"
- "multi-step process"
- "multi step process"
- "multi-step creation"
- "multi-step generation"
- "processing pipeline"
- "creation pipeline"
- "generation pipeline"
- "content pipeline"
- "production pipeline"
- "approval pipeline"
- "ingestion pipeline"
- "streams progress"
- "stream progress"
- "streams each phase"
- "streams each step"
- "streams each"
- "stream each"
# Reliability / durability language (missed in customer-support eval)
- "survive page reload"
- "survive page reloads"
- "survive a crash"
- "survive crashes"
- "survive network"
- "fault-tolerant"
- "fault tolerant"
- "crash-safe"
- "crash safe"
- "automatically retry"
- "auto retry"
- "retry on failure"
- "retry on error"
- "reliable and retry"
- "reliable processing"
- "individually reliable"
- "each step reliable"
- "each step should be reliable"
- "steps should be reliable"
- "reliable with automatic retry"
- "reliable with retry"
- "retry on transient"
- "transient failures"
- "session persistence"
- "session should persist"
- "session survives"
- "reconnect automatically"
- "auto reconnect"
- "reconnect if the network"
- "reconnect on disconnect"
- "resume after failure"
- "resume after crash"
- "resume on reconnect"
# Human-in-the-loop / approval patterns
- "human-in-the-loop"
- "human in the loop"
- "wait for approval"
- "approval step"
- "approval before"
- "editorial approval"
- "manual approval"
- "wait for user"
- "pause until"
- "wait for response"
- "callback url"
- "webhook callback"
# Conversational AI with durability
- "chat should survive"
- "chat survives"
- "conversation should persist"
- "conversation persists"
- "conversation should survive"
# Sequential / chain / trigger orchestration language
- "sequential chain"
- "email chain"
- "chain of emails"
- "chain of steps"
- "chain engine"
- "chain with triggers"
- "trigger chain"
- "triggered chain"
- "webhook chain"
- "webhook pipeline"
- "webhook orchestration"
- "multi-service trigger"
- "cross-service trigger"
- "various triggers"
- "different triggers"
- "triggers from different"
- "triggers from various"
- "sequential steps"
- "sequential pipeline"
- "sequential process"
- "sequential emails"
- "escalation chain"
- "escalation pipeline"
- "state machine"
- "step-based"
- "step based"
- "delay between steps"
- "delay between emails"
- "delayed steps"
- "conditional steps"
- "skip steps"
- "branch based on"
- "wait for webhook"
- "wait for trigger"
- "wait for event"
- "orchestrate emails"
- "orchestrate webhooks"
- "orchestrate services"
- "chain across services"
# Debugging
- "workflow stuck"
- "workflow hung"
- "workflow hanging"
- "workflow waiting"
- "workflow failing"
- "workflow timeout"
- "workflow not running"
- "workflow error"
- "check workflow"
- "workflow logs"
- "workflow run status"
- "debug workflow"
- "workflow not finishing"
- "workflow not responding"
- "workflow stalled"
- "workflow pending"
- "step is stuck"
- "step is hanging"
- "why is my workflow"
- "workflow run"
- "step failed"
- "run status"
- "run failed"
- "run logs"
- "workflow run failed"
- "workflow step failed"
allOf:
- [workflow, durable]
- [workflow, retry]
- [workflow, resume]
- [pause, resume]
- [survive, crash]
- [survive, reload]
- [survive, disconnect]
- [pipeline, stream]
- [pipeline, step]
- [pipeline, durable]
- [pipeline, reliable]
- [pipeline, retry]
- [multi-step, stream]
- [multi-step, reliable]
- [generation, pipeline]
- [creation, pipeline]
- [process, stream]
- [process, reliable]
- [process, retry]
- [retry, failure]
- [retry, error]
- [retry, automatically]
- [retry, transient]
- [reliable, retry]
- [individually, reliable]
- [steps, reliable]
- [sandbox, reliable]
- [sandbox, retry]
- [reconnect, network]
- [reconnect, drop]
- [reconnect, disconnect]
- [session, persist]
- [session, survive]
- [session, reload]
- [session, reconnect]
- [chat, survive]
- [chat, persist]
- [chat, reconnect]
- [chat, durable]
- [chat, fault]
- [conversation, persist]
- [conversation, survive]
- [approval, wait]
- [approval, human]
- [each, step]
- [each, phase]
- [each, stage]
- [step, reliable]
- [step, retry]
# Chain / trigger / sequential orchestration
- [chain, trigger]
- [chain, sequential]
- [chain, email]
- [chain, webhook]
- [chain, delay]
- [chain, step]
- [chain, escalat]
- [sequential, trigger]
- [sequential, email]
- [sequential, step]
- [sequential, webhook]
- [trigger, orchestrat]
- [trigger, service]
- [trigger, delay]
- [trigger, sequential]
- [webhook, chain]
- [webhook, orchestrat]
- [webhook, pipeline]
- [webhook, sequential]
- [email, trigger]
- [email, pipeline]
- [email, sequential]
- [email, delay]
- [email, escalat]
- [escalat, trigger]
- [escalat, step]
- [escalat, email]
- [state, machine]
- [conditional, step]
- [conditional, skip]
- [branch, condition]
- [wait, webhook]
- [wait, trigger]
- [wait, event]
- [workflow, stuck]
- [workflow, hung]
- [workflow, timeout]
- [workflow, error]
- [workflow, logs]
- [workflow, debug]
- [workflow, check]
- [workflow, failing]
- [workflow, status]
- [run, status]
- [step, failed]
- [step, stuck]
- [step, timeout]
- [workflow, run]
- [run, logs]
anyOf:
- "long-running"
- "long running"
- "multi-step"
- "multi step"
- "pipeline"
- "orchestration"
- "step-by-step"
- "step by step"
- "each piece"
- "each step"
- "each phase"
- "each stage"
- "phase"
- "phases"
- "stage"
- "stages"
- "durable"
- "reliable"
- "fault-tolerant"
- "retry"
- "reconnect"
- "survive"
- "persist"
- "approval"
- "chain"
- "sequential"
- "trigger"
- "webhook"
- "escalation"
- "state machine"
- "orchestrate"
- "orchestration"
noneOf:
- "github actions"
- ".github/workflows"
- "ci workflow"
- "aws step functions"
minScore: 4
validate:
-
pattern: experimental_createWorkflow
message: 'experimental_createWorkflow is now stable — use createWorkflow from @vercel/workflow. Run npx @ai-sdk/codemod v6 for automated migration.'
severity: error
upgradeToSkill: workflow
upgradeWhy: 'Guides migration from experimental_createWorkflow to the stable createWorkflow API and then to the "use workflow" directive.'
-
pattern: from\s+['"]@vercel/workflow['"]
message: 'Workflow SDK requires AI Gateway OIDC setup — ensure vercel link + vercel env pull for VERCEL_OIDC_TOKEN'
severity: recommended
-
pattern: setTimeout|setInterval
message: 'setTimeout/setInterval are not available in workflow sandbox scope — use sleep() from "workflow" for delays'
severity: error
skipIfFileContains: "use step"
-
pattern: context\.run\s*\(
message: 'context.run() is not a Workflow SDK pattern — use "use step" directive for retryable, observable steps'
severity: error
upgradeToSkill: workflow
upgradeWhy: 'Guides migration from context.run() to the "use step" directive for durable, retryable workflow steps.'
-
pattern: \brequire\s*\(
message: 'require() is not available in workflow sandbox scope — use ESM imports and move Node.js logic into "use step" functions'
severity: error
skipIfFileContains: "use step"
-
pattern: getWritable\(\)
message: 'getWritable() must only be called inside "use step" functions — workflow sandbox scope does not support it'
severity: recommended
skipIfFileContains: "use step"
-
pattern: createWorkflow\s*\(
message: 'createWorkflow() is the legacy API — use the "use workflow" directive on an async function instead'
severity: error
upgradeToSkill: workflow
upgradeWhy: 'Guides migration from createWorkflow() function API to the "use workflow" directive pattern.'
skipIfFileContains: experimental_createWorkflow
-
pattern: streamObject\s*\(
message: 'streamObject() was removed in AI SDK v6 — use streamText() with output: Output.object() instead'
severity: error
upgradeToSkill: ai-sdk
upgradeWhy: 'Guides migration from streamObject to streamText + Output.object() with correct v6 streaming patterns.'
-
pattern: await\s+\w+Workflow\s*\(
message: 'Do not call workflow functions directly — use start() from "workflow/api" to register the run and get a runId'
severity: recommended
skipIfFileContains: "use workflow"
-
pattern: \bfetch\s*\(
message: 'Native fetch() is not available in workflow sandbox scope — import fetch from "workflow" or move the call into a "use step" function'
severity: recommended
skipIfFileContains: "use step"
-
pattern: '"use step"'
message: "Workflow steps should include console.log or structured logging for observability — add logging at step entry/exit to debug hangs"
severity: warn
skipIfFileContains: "console\\.(log|warn|error|info)"
-
pattern: '"use workflow"'
message: "Workflow files should import and use logging — add console.log or a logger at key execution points for debugging"
severity: warn
skipIfFileContains: "console\\.(log|warn|error|info)"
chainTo:
-
pattern: 'DurableAgent|@workflow/ai'
targetSkill: ai-sdk
message: 'DurableAgent detected without AI SDK context — loading AI SDK guidance for tool calling, Agent class, and model configuration.'
skipIfFileContains: 'from\s+[''"]ai[''"]|@ai-sdk/|streamText|generateText'
-
pattern: 'process\.env\.(OPENAI_API_KEY|ANTHROPIC_API_KEY)|from\s+[''"]@ai-sdk/(anthropic|openai)[''""]'
targetSkill: ai-gateway
message: 'Direct provider API key in workflow — loading AI Gateway guidance for OIDC auth (required for Workflow SDK AI steps).'
skipIfFileContains: 'gateway\(|@ai-sdk/gateway|VERCEL_OIDC'
-
pattern: 'setTimeout\s*\(|setInterval\s*\('
targetSkill: vercel-functions
message: 'Timer-based delay in workflow code — use sleep() from "workflow" instead of setTimeout/setInterval. Loading Vercel Functions guidance.'
skipIfFileContains: 'from\s+[''"]workflow[''"].*sleep|sleep\s*\('
retrieval:
aliases:
- durable workflow
- long running task
- step function
- orchestration
intents:
- build workflow
- add retry logic
- create durable task
- implement step function
entities:
- Workflow SDK
# Legacy product names retained only as retrieval aliases.
- Workflow DevKit
- WDK
- step
- pause/resume
- durable
---
## *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:**
```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";
// Analytics API
import { getWorld } from "workflow/runtime";
// 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.
```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. Deterministic tokens are for `createHook()` + `resumeHook()` (server-side) only. `createWebhook()` always generates random tokens — do not pass a `token` option to `createWebhook()`.
### 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 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 body using computed property syntax:
```typescript
import { WORKFLOW_SERIALIZE, WORKFLOW_DESERIALIZE } from "@workflow/serde";
export class Point {
x: number;
y: number;
constructor(x: number, y: number) {
this.x = x;
this.y = y;
}
// Serialize: return plain data (must be devalue-compatible types only)
static [WORKFLOW_SERIALIZE](instance: Point) {
return { x: instance.x, y: instance.y };
}
// Deserialize: reconstruct from plain data
static [WORKFLOW_DESERIALIZE](data: { x: number; y: number }) {
return new Point(data.x, data.y);
}
async computeDistance(other: Point) {
"use step";
return Math.sqrt((this.x - other.x) ** 2 + (this.y - other.y) ** 2);
}
}
```
**Critical rules:**
1. **Define serde methods INSIDE the class body** as static methods with computed property syntax (`static [WORKFLOW_SERIALIZE](...)`). The SWC plugin detects them by scanning the class. Do NOT assign them externally (e.g., `(MyClass as any)[WORKFLOW_SERIALIZE] = ...`) -- the compiler will not detect this.
2. **Serde methods must return only devalue-compatible types** (plain objects, arrays, primitives, Date, Map, Set, Uint8Array, etc.). No functions, no class instances, no Node.js-specific objects.
3. **Add `"use step"` to Node.js-dependent instance methods.** The SWC plugin strips `"use step"` method bodies from the workflow bundle. This is how you keep Node.js imports (fs, crypto, child_process, etc.) out of the workflow sandbox. The class shell with its serde methods remains in the workflow bundle; only the step method bodies are removed.
4. **Do NOT manually register classes.** The SWC plugin automatically generates registration code (an IIFE that sets `classId` and adds the class to the global registry). Manual calls to `registerSerializationClass()` are unnecessary and error-prone.
5. **Do NOT use dynamic imports to work around sandbox restrictions.** If a class method needs Node.js APIs, the correct solution is `"use step"`, not `/* @vite-ignore */ import(...)`.
**When serde works well:** Pure data classes, domain models, configuration objects, and classes where Node.js-dependent methods can be marked with `"use step"`.
**When to avoid serde:** If a class is fundamentally inseparable from Node.js APIs (every method needs `fs`, `net`, etc.) and cannot meaningfully exist as a shell in the workflow sandbox, keep it entirely in step functions and pass plain data objects across boundaries instead.
### Validating Serde Compliance
Use these tools to verify classes are correctly set up:
- **`workflow transform <file> --check-serde`** -- Shows the SWC transform output for a file and checks if serde classes are compliant (no Node.js imports remaining in the workflow bundle).
- **`workflow validate`** -- Scans all workflow files and reports serde compliance issues. Use `--json` for machine-readable output.
- **SWC Playground** -- The web playground at `workbench/swc-playground` shows a Serde Analysis panel when serde patterns are detected.
- **Build-time warnings** -- The builder automatically warns when serde classes have Node.js built-in imports remaining in the workflow bundle.
## 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();
}
}
```
### Namespaced Streams
Use `getWritable({ namespace: 'name' })` to create multiple independent streams for different types of data. This is useful for separating logs from primary output, different log levels, agent outputs, metrics, or any distinct data channels. Long-running workflows benefit from namespaced streams because you can replay only the important events (e.g., final results) while keeping verbose logs in a separate stream.
**Example: Log levels and agent output separation:**
```typescript
import { getWritable } from "workflow";
type LogEntry = { level: "debug" | "info" | "warn" | "error"; message: string; timestamp: number };
type AgentOutput = { type: "thought" | "action" | "result"; content: string };
async function logDebug(message: string) {
"use step";
const writer = getWritable<LogEntry>({ namespace: "logs:debug" }).getWriter();
try {
await writer.write({ level: "debug", message, timestamp: Date.now() });
} finally {
writer.releaseLock();
}
}
async function logInfo(message: string) {
"use step";
const writer = getWritable<LogEntry>({ namespace: "logs:info" }).getWriter();
try {
await writer.write({ level: "info", message, timestamp: Date.now() });
} finally {
writer.releaseLock();
}
}
async function emitAgentThought(thought: string) {
"use step";
const writer = getWritable<AgentOutput>({ namespace: "agent:thoughts" }).getWriter();
try {
await writer.write({ type: "thought", content: thought });
} finally {
writer.releaseLock();
}
}
async function emitAgentResult(result: string) {
"use step";
// Important results go to the default stream for easy replay
const writer = getWritable<AgentOutput>().getWriter();
try {
await writer.write({ type: "result", content: result });
} finally {
writer.releaseLock();
}
}
export async function agentWorkflow(task: string) {
"use workflow";
await logInfo(`Starting task: ${task}`);
await logDebug("Initializing agent context");
await emitAgentThought("Analyzing the task requirements...");
// ... agent processing ...
await emitAgentResult("Task completed successfully");
await logInfo("Workflow finished");
}
```
**Consuming namespaced streams:**
```typescript
import { start, getRun } from "workflow/api";
import { agentWorkflow } from "./workflows/agent";
export async function POST(request: Request) {
const run = await start(agentWorkflow, ["process data"]);
// Access specific streams by namespace
const results = run.getReadable({ namespace: undefined }); // Default stream (important results)
const infoLogs = run.getReadable({ namespace: "logs:info" });
const debugLogs = run.getReadable({ namespace: "logs:debug" });
const thoughts = run.getReadable({ namespace: "agent:thoughts" });
// Return only important results for most clients
return new Response(results, { headers: { "Content-Type": "application/json" } });
}
// Resume from a specific point (useful for long sessions)
export async function GET(request: Request) {
const { searchParams } = new URL(request.url);
const runId = searchParams.get("runId")!;
const startIndex = parseInt(searchParams.get("startIndex") || "0", 10);
const run = getRun(runId);
// Resume only the important stream, skip verbose debug logs
const stream = run.getReadable({ startIndex });
return new Response(stream);
}
```
**Pro tip:** For very long-running sessions (50+ minutes), namespaced streams help manage replay performance. Put verbose/debug output in separate namespaces so you can replay just the important events quickly.
## 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
```
### Deep-linking to a run (share a URL, no browser)
Use `--url` to **print** the dashboard deep link and exit — no browser opens and
no local server starts. This is the right tool when you need to hand a user a
clickable link (PR comment, Slack message, debugging summary) rather than open a
UI. (`--web` opens the dashboard; `--url` only prints the link.)
```bash
# Vercel run — prints the Vercel dashboard URL for the run
npx workflow inspect run <run_id> --backend vercel --project <project> --team <team> --url
npx workflow web <run_id> --backend vercel --project <project> --team <team> --env preview --url
# Local run — prints the local web UI deep link
npx workflow inspect run <run_id> --url
# Machine-readable: --url --json prints { "url": "..." } to stdout
npx workflow inspect run <run_id> --backend vercel --url --json
```
URL formats produced:
- **Vercel:** `https://vercel.com/<team-slug>/<project-slug>/workflows/runs/<run_id>?environment=<production|preview>`
(`--env` selects the environment; defaults to `production`. Resolving the team
slug requires being logged in via `vercel login` with the project linked.)
- **Local:** `http://localhost:<port>?resource=run&id=<run_id>` (port defaults
to `3456`; the link works while the `npx workflow web` server is running).
stdout contains **only** the URL (or the JSON object) — all other output goes to
stderr — so you can capture it directly, e.g. `URL=$(npx workflow web <run_id> --backend vercel --url)`.
**Debugging tips:**
- Use `--json` (`-j`) on any command for machine-readable output
- Use `--web` to open the Vercel Observability dashboard in your browser, or `--url` to just print the deep link
- Use `--help` on any command for full usage details
- Only import workflow APIs you actually use. Unused imports can cause 500 errors.
## Testing Workflows
Workflow SDK provides a Vitest plugin for testing workflows in-process — no running server required.
**Unit testing steps:** Steps are just functions; without the compiler, `"use step"` is a no-op. Test them directly:
```typescript
import { describe, it, expect } from "vitest";
import { createUser } from "./user-signup";
describe("createUser step", () => {
it("should create a user", async () => {
const user = await createUser("test@example.com");
expect(user.email).toBe("test@example.com");
});
});
```
**Integration testing:** Use `@workflow/vitest` for workflows using `sleep()`, hooks, webhooks, or retries:
```typescript
// vitest.integration.config.ts
import { defineConfig } from "vitest/config";
import { workflow } from "@workflow/vitest";
export default defineConfig({
plugins: [workflow()],
test: {
include: ["**/*.integration.test.ts"],
testTimeout: 60_000,
},
});
```
```typescript
// approval.integration.test.ts
import { describe, it, expect } from "vitest";
import { start, getRun, resumeHook } from "workflow/api";
import { waitForHook, waitForSleep } from "@workflow/vitest";
import { approvalWorkflow } from "./approval";
describe("approvalWorkflow", () => {
it("should publish when approved", async () => {
const run = await start(approvalWorkflow, ["doc-123"]);
// Wait for the hook, then resume it
await waitForHook(run, { token: "approval:doc-123" });
await resumeHook("approval:doc-123", { approved: true, reviewer: "alice" });
// Wait for sleep, then wake it up
const sleepId = await waitForSleep(run);
await getRun(run.runId).wakeUp({ correlationIds: [sleepId] });
const result = await run.returnValue;
expect(result).toEqual({ status: "published", reviewer: "alice" });
});
});
```
**Testing webhooks:** Use `resumeWebhook()` with a `Request` object — no HTTP server needed:
```typescript
import { start, resumeWebhook } from "workflow/api";
import { waitForHook } from "@workflow/vitest";
const run = await start(ingestWorkflow, ["ep-1"]);
const hook = await waitForHook(run); // Discovers the random webhook token
await resumeWebhook(hook.token, new Request("https://example.com/webhook", {
method: "POST",
body: JSON.stringify({ event: "order.created" }),
}));
```
**Key APIs:**
- `start()` — trigger a workflow
- `run.returnValue` — await workflow completion
- `waitForHook(run, { token? })` / `waitForSleep(run)` — wait for workflow to reach a pause point
- `resumeHook(token, data)` / `resumeWebhook(token, request)` — resume paused workflows
- `getRun(runId).wakeUp({ correlationIds })` — skip `sleep()` calls
**Best practices:**
- Keep unit tests (no plugin) and integration tests (`workflow()` plugin) in separate configs
- Use deterministic hook tokens based on test data for easier resumption
- Set generous `testTimeout` — workflows may run longer than typical unit tests
- `vi.mock()` does **not** work in integration tests — step dependencies are bundled by esbuild
## Observability & World SDK
Use `await getWorld()` to build observability dashboards, admin panels, and inspect workflow state. `getWorld()` is asynchronous and returns `Promise<World>` (dynamic import / env-based setup).
**Key imports:**
```typescript
import { getWorld } from "workflow/runtime";
import { hydrateResourceIO, observabilityRevivers, parseStepName, parseWorkflowName } from "workflow/observability";
```
**Key docs** (grep `node_modules/workflow/docs/` for full details):
- `api-reference/workflow-runtime/world/storage.mdx` — events, runs, steps, hooks (events are source of truth; others are materialized views)
- `api-reference/workflow-observability/` — hydration and name parsing
### World SDK Method Signatures
⚠️ Pagination is nested: `{ pagination: { cursor } }` — NOT `{ cursor }` directly.
```typescript
const world = await getWorld();
// Runs
const { data, cursor } = await world.runs.list({ pagination: { cursor }, resolveData: 'all' | 'none' });
const run = await world.runs.get(runId, { resolveData: 'all' | 'none' });
// Cancel via event creation (no cancel() method on runs)
await world.events.create(runId, { eventType: 'run_cancelled' });
// Steps — runId is top-level, NOT inside pagination
const { data, cursor } = await world.steps.list({ runId, pagination: { cursor }, resolveData: 'all' | 'none' });
const step = await world.steps.get(runId, stepId, { resolveData: 'all' | 'none' });
// Events
const { data, cursor } = await world.events.list({ runId, pagination: { cursor } });
await world.events.create(runId, { eventType: 'run_cancelled' });
// Hooks
const hook = await world.hooks.get(hookId);
const hook = await world.hooks.getByToken(token);
// Streams (methods on world.streams)
await world.streams.write(runId, name, chunk);
await world.streams.writeMulti?.(runId, name, chunks);
const readable = await world.streams.get(runId, name, startIndex);
await world.streams.close(runId, name);
const streamNames = await world.streams.list(runId);
const chunks = await world.streams.getChunks(runId, name, { limit, cursor });
const info = await world.streams.getInfo(runId, name);
// Queue (methods live directly on world — internal SDK infrastructure)
await world.queue(queueName, payload, opts);
const deploymentId = await world.getDeploymentId();
```
### `resolveData` Parameter
Controls whether input/output data is **included** in the response. Accepts `'all'` (default) or `'none'`.
**IMPORTANT**: Even with `'all'`, data is still devalue-serialized. You MUST call `hydrateResourceIO()` to get usable JS values.
- **Use `'none'`** for status polling, progress dashboards, run listings
- **Use `'all'`** (or omit) when you need to inspect actual step I/O data — then **always hydrate**
```typescript
// Lightweight status check — no I/O loaded
const run = await world.runs.get(runId, { resolveData: 'none' });
console.log(run.status); // 'running' | 'completed' | 'failed' | 'cancelled'
// Full inspection — resolveData includes data, hydrateResourceIO deserializes it
const step = await world.steps.get(runId, stepId); // defaults to 'all'
const hydrated = hydrateResourceIO(step, observabilityRevivers);
```
> **Common mistake**: Checking `step.input !== undefined` after `resolveData: 'all'` and assuming
> the data is ready to use. The data exists but is serialized — always hydrate first.
### Data Hydration (Devalue Format)
Step I/O is serialized via [devalue](https://github.com/Rich-Harris/devalue) with a 4-byte format prefix (`devl`). Without hydration, `input`/`output` are Uint8Array-like objects with numeric keys:
`{"0":100,"1":101,"2":118,"3":108,...}` — these are NOT usable values.
**Always hydrate before using I/O data:**
```typescript
import { hydrateResourceIO, observabilityRevivers } from "workflow/observability";
const { data: steps } = await world.steps.list({ runId, resolveData: 'all' });
const hydrated = steps.map(s => hydrateResourceIO(s, observabilityRevivers));
// hydrated[0].input → [123, 2] (actual function arguments)
// hydrated[0].output → 125 (actual return value)
```
`hydrateResourceIO` works on both `Step` and `WorkflowRun` objects. For encrypted workflows, use `getEncryptionKeyForRun()` + `hydrateResourceIOWithKey()`.
### Name Parsing
`parseWorkflowName()`, `parseStepName()`, and `parseClassName()` return `{ shortName: string, moduleSpecifier: string } | null`. Always use optional chaining:
```typescript
const parsed = parseWorkflowName("workflow//./src/workflows/order//processOrder");
// parsed?.shortName → "processOrder"
// parsed?.moduleSpecifier → "./src/workflows/order"
// ⚠️ Returns null if format doesn't match
```
### Event Types
Events are the append-only source of truth. Runs/Steps/Hooks are materialized views.
| Category | Types |
|----------|-------|
| Run | `run_created`, `run_started`, `run_completed`, `run_failed`, `run_cancelled` |
| Step | `step_created`, `step_started`, `step_completed`, `step_failed`, `step_retrying` |
| Hook | `hook_created`, `hook_received`, `hook_disposed`, `hook_conflict` |
| Wait | `wait_created`, `wait_completed` |
## Error Handling Patterns
Three error strategies for different failure modes:
| Error Type | Use When | Behavior |
|------------|----------|----------|
| `FatalError` | Permanent failure (bad input, auth denied) | Terminates workflow immediately, no retry |
| `RetryableError` | Transient failure (rate limit, timeout) | Retries with optional `retryAfter` delay |
| `Promise.allSettled` | Parallel steps with mixed criticality | Continues even if some steps fail |
```typescript
import { FatalError, RetryableError } from "workflow";
// Permanent failure — workflow terminates
throw new FatalError("Invalid input: missing required field");
// Transient failure — will retry
throw new RetryableError("API rate limited", { retryAfter: "5m" });
// Mixed criticality parallel execution
const results = await Promise.allSettled([
criticalStep(data), // Must succeed
optionalStep(data), // OK to fail
enrichmentStep(data), // OK to fail
]);
const [critical, optional, enrichment] = results;
if (critical.status === "rejected") throw new FatalError(critical.reason);
```
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