> ## Documentation Index
> Fetch the complete documentation index at: https://openworkflow.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Overview

> How OpenWorkflow works and how Workflows, Steps, and Workers fit together

This page explains the mental model behind OpenWorkflow. For setup and command
examples, see [Quick Start](/docs/quickstart) and the linked detail pages.

## Building Blocks

OpenWorkflow has three core building blocks:

* **Workflows**: durable functions that describe your business process
* **Steps**: durable checkpoints that memoize results and protect side effects
* **Workers**: stateless processes that execute and resume workflow runs

Your application enqueues workflow runs. Workers pick them up. The backend
(PostgreSQL or SQLite) stores durable state and coordinates recovery.

## Lifecycle

When a run starts:

1. Your app enqueues a run (for example, with `ow.runWorkflow(workflow.spec,
   input)`), creating a `pending` run in the database
2. A worker claims the run and marks it `running`
3. The worker replays workflow code from the beginning
4. Completed steps return cached outputs; new steps execute and persist results
5. The run transitions to `completed`, `failed`, or `canceled` (or stays
   `running` while durably parked for sleep)

Because replay is deterministic, crash recovery is reliable. A replacement
worker can continue from the last durable checkpoint without redoing completed
work.

## Why This Is Reliable

* **Memoized steps** prevent duplicate side effects on retries
* **Durable sleep** (`step.sleep`) pauses runs without holding worker capacity
* **Signals** (`step.sendSignal`, `step.waitForSignal`) enable runtime
  communication to & between workflows
* **Heartbeats + leases** (`availableAt`) allow automatic crash recovery
* **Database as source of truth** avoids a separate orchestration service

## Read Next

* [Workflows](/docs/workflows): define and run workflows, options, and states
* [Steps](/docs/steps): step types, naming, and retry behavior
* [Workers](/docs/workers): execution model, concurrency, and graceful shutdown
* [Configuration](/docs/configuration): config file and worker/backend settings