---
title: 'Should I build an agent or a workflow?'
description: 'An agent holds a conversation and decides what to call. A workflow runs a fixed pipeline that has to finish.'
position: 1
---

# Should I build an agent or a workflow?

> Ask who is driving. If a person is talking to it and the next move depends on
> the reply, build an **agent**. If it is a job with a start and an end that has
> to finish whatever happens, build a **workflow**.

An agent is open-ended. You declare it with `defineDeepAgent(...)`: a model, a
system prompt and tools. The model decides which tool to call from the name,
description and schema you gave each one. It keeps the thread across turns and
the runtime serves it over the standard chat endpoints, so the conversation is
the unit of work.

A workflow is fixed and auditable: validate, call a model, write a side effect.
Each `'use step'` runs once, persists its result, and retries on failure. The
run survives crashes and redeploys and can pause for months waiting on a sleep
or a human decision.

You can mix the two. A workflow step can hand a turn to an agent with
`callDeepAgent(name, input)`, which is the common shape when a pipeline needs
one piece of judgement in the middle. One rule applies to both: touch
`stackbone.*` only inside a step, never in the workflow body.

## Read more

- **[Agents](/docs/sdk/agents/overview)**: the authoring model and the tools an
  agent calls.
- **[Workflows](/docs/sdk/workflows/overview)**: `'use workflow'`, `'use step'`
  and what replay means for your code.
- **[Workflow + Agents](/docs/sdk/workflow-agents/overview)**: delegating a turn
  to an agent from inside a step.