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

# Application resources

> Start dependencies once, publish them to agent code, and close them safely.

Use lifecycle resources for database pools, service clients, caches, and other application-owned dependencies.

```python theme={null}
from harnest.context import context
from harnest.lifecycle import lifecycle
from harnest.lib.catalog import CatalogClient


@lifecycle.resource
@context("catalog")
async def catalog():
    client = CatalogClient()
    try:
        yield client
    finally:
        await client.close()
```

## Resource properties

| Decorator             | Lifetime    | Visible to agent code? |
| --------------------- | ----------- | ---------------------: |
| `@lifecycle.resource` | Application |                     No |
| Both decorators       | Application |                    Yes |
| `@context("name")`    | Invocation  |                    Yes |

Harnest starts application resources in order and closes them in reverse order.

## Read a resource

```python theme={null}
from harnest import context


def search_catalog(query: str):
    catalog = context.resource("catalog")
    return catalog.search(query)
```

| Rule              | Result                                        |
| ----------------- | --------------------------------------------- |
| Unique name       | Duplicate context resources fail compilation  |
| Active invocation | Access outside an invocation fails            |
| Root ownership    | SubAgents use the root binding                |
| No credentials    | Resolve secrets through `context.credentials` |

## Resource or tool?

| Need                              | Choose              |
| --------------------------------- | ------------------- |
| Dependency used by trusted Python | Resource            |
| Capability the model can invoke   | Agent Tool          |
| Downstream secret or user token   | Credential provider |
| Session or checkpoint persistence | Storage factory     |

<CardGroup cols={2}>
  <Card title="Agent Tools" icon="wrench" href="/harnest/build/agent-tools">
    Expose typed capabilities to the model.
  </Card>

  <Card title="Auth and credentials" icon="key" href="/harnest/runtime/authentication-and-credentials">
    Resolve private credentials inside an invocation.
  </Card>
</CardGroup>