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

# Extend a workflow

> Inject custom logic into an existing Mercur workflow through hooks — without rewriting it.

<Note>
  This guide is being written. The outline below is the intended structure.
</Note>

<Info>
  **Workflows are Medusa's extension model — Mercur keeps it.** Unlike the panels (where Mercur ships [its own customization framework](/rc/resources/customization/extending-panels)), backend logic follows Medusa conventions unchanged: Mercur's workflows expose hooks you inject steps into, with the same compensation/rollback semantics as any Medusa workflow. Skills learned in plain Medusa transfer here one-to-one.
</Info>

## Why hooks

Extend behavior without forking or rewriting the workflow.

<Steps>
  <Step title="Pick the target hook">
    The `completeCartWithSplitOrdersWorkflow` and where its hooks sit.
  </Step>

  <Step title="Inject a step">
    The shape of a hook and how to register your step.
  </Step>

  <Step title="Handle compensation and rollback">
    How your step participates in automatic rollback on failure.
  </Step>
</Steps>

## Verify

Confirm the injected behavior runs and rolls back correctly.

## Next steps

<CardGroup cols={2}>
  <Card title="Add a custom API route" href="/rc/resources/tutorials/custom-api-route" />

  <Card title="Custom fields" href="/rc/resources/customization/custom-fields" />
</CardGroup>