Workflows

A workflow is a named sequence of steps with a validated input schema. Any Standard Schema-compatible library works (Zod, Valibot, ArkType, …).

import { createWorkflow } from 'reflow-ts'
import { z } from 'zod'

const workflow = createWorkflow({
  name: 'send-welcome',
  input: z.object({ userId: z.string(), email: z.email() }),
})
  .step('create-account', async ({ input }) => {
    // input is typed as { userId: string; email: string }
    return { accountId: await createAccount(input.userId) }
  })
  .step('send-email', async ({ prev, input, signal }) => {
    // prev is typed as { accountId: string }
    await sendEmail(input.email, `Welcome! Your account: ${prev.accountId}`, { signal })
  })

The step context

Each .step() handler receives a single context object:

Field	Description
input	The validated workflow input. The same value for every step in the run.
prev	The return value of the previous step (undefined for the first step).
steps	Typed access to all previously completed step results by name, e.g. steps.charge.chargeId.
signal	An AbortSignal, aborted when the run is cancelled, its lease is lost, or the step times out.
complete(value?)	Finish the workflow early, skipping remaining steps. See Early Completion.

prev vs steps

prev is the most recent step's output. steps is the full history — reach any earlier step directly without forwarding data through every intermediate step:

const workflow = createWorkflow({ name: 'pipeline', input: schema })
  .step('fetch', async ({ input }) => {
    return { url: input.url, body: await fetchPage(input.url) }
  })
  .step('parse', async ({ prev }) => {
    return { title: extractTitle(prev.body), links: extractLinks(prev.body) }
  })
  .step('save', async ({ steps }) => {
    // Access any previous step directly — no forwarding needed
    await save(steps.fetch.url, steps.parse.title, steps.parse.links)
  })

The steps object is a frozen, deep-cloned snapshot. Mutating prev in one step never affects what later steps see through steps.

Persistable values

Step inputs and outputs are persisted, so they must be plain data: objects, arrays, strings, numbers, booleans, null, undefined, and Date. Returning a non-serializable value (a function, a class instance, NaN) throws a SerializationError.

The builder is immutable

Each .step() returns a new workflow instance, so you can branch safely:

const base = createWorkflow({ name: 'base', input: z.object({}) })
const withLogging = base.step('log', async () => { /* … */ })
const withMetrics = base.step('metric', async () => { /* … */ })
// base, withLogging, and withMetrics are independent

Step names must be unique within a workflow — reusing one throws DuplicateStepError.

Next

• The Engine — run your workflows.
• Retry & Timeouts, Parallel Steps, Early Completion.