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

# Service

> API reference for uniac.Service.

`uniac.Service` is the base class for `kind=lib` packages — reusable building blocks consumed by other Services or Systems. It is a pure marker subclass of [`NodeSpec`](/sdk/nodespec): no `__init__`, no methods to override.

```python theme={null}
from uniac import Service
```

## Declaring a Service

Subclass `Service` and declare any [`Node`](/sdk/node) dependencies as class-level annotations. If you take init args, provide your own `__init__`.

```python theme={null}
from uniac import Service
from db import Db  # generated Node stub

class Cache(Service):
    db: Db

    def __init__(self, ttl_seconds: int = 60):
        self.db = Db()
        self.ttl_seconds = ttl_seconds
```

`uniac build` publishes this Service to the local store. Other packages list its name under `dependencies` in [`uniac.json`](/concepts/manifest), run `uniac install`, and import a generated `Cache` Node stub.

## What `Service` provides

* `_uniac_validate()` — inherited from [`NodeSpec`](/sdk/nodespec).
* `_uniac_walk()` — inherited from [`NodeSpec`](/sdk/nodespec).

There is **no** base-class `__init__` to call. The framework never auto-instantiates Nodes; you do.

For deployable packages, use [`System`](/sdk/system) instead.