# Overview

The four ideas used throughout Workers IO docs.

Workers IO docs use four core ideas: workloads, mocks, faults, and simulations. These are the pieces you define to turn one important product behavior into many realistic runs.

## Workloads

A workload is the command that drives behavior your users depend on. It sets up state, performs operations, and checks invariants.

Read [Test Workloads](/docs/workloads/) to design one.

## Mocks

Mocks describe external service behavior. Use them for APIs, webhooks, providers, and services you do not want the run to call directly.

The project-level mock file is:

```text
.workers/external-mocks.json
```

Read [Mocks](/docs/mocks/) to model external services.

## Faults

Faults describe operating conditions the workflow should survive. Network faults are available today; storage, service shutdown, resource pressure, and scheduler pressure faults are coming soon.

Named CLI network faults live under:

```text
.workers/fault/net/
```

Read [Faults](/docs/faults/) to model operating conditions.

## Simulations

A simulation runs one workload across seeds and fault models. Each seed explores a different scenario. Each failure gives you logs, captured inputs, artifacts, and the exact workload and fault context used for the run.

Read [Simulations](/docs/simulations/) to run workloads, inspect failures, rerun cases, and verify fixes.