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

# eos

> The default Effect-aware oRPC builder.

`eos` is the default Effect-aware procedure builder exported from `effect-orpc`.

```ts title="import.ts" theme={null}
import { eos } from "effect-orpc";
```

## Basic use

```ts title="basic.ts" theme={null}
const effectProcedure = eos.provide(AppLive);

const procedure = effectProcedure.effect(function* () {
  const usersRepo = yield* UsersRepo;
  return yield* usersRepo.list();
});
```

`eos` starts without an application layer. Most apps call `.provide(AppLive)` once and reuse the returned builder.

Effect-native callbacks on the builder can be generator functions or functions that return an `Effect`.

## Common methods

| Method                      | Purpose                                                |
| --------------------------- | ------------------------------------------------------ |
| `.$context<T>()`            | Set the initial oRPC context type.                     |
| `.provide(layer)`           | Provide a base Effect layer.                           |
| `.provide(tag, fn)`         | Provide a request-scoped service.                      |
| `.provideOptional(tag, fn)` | Optionally provide a request-scoped service.           |
| `.errors(map)`              | Add oRPC and tagged Effect errors.                     |
| `.input(schema)`            | Define input validation.                               |
| `.output(schema)`           | Define output validation.                              |
| `.use(middleware)`          | Add native, generator, or Effect-returning middleware. |
| `.traced(name)`             | Override the Effect span name.                         |
| `.handler(fn)`              | Define a standard oRPC handler.                        |
| `.effect(fn)`               | Define an Effect handler.                              |
| `.prefix(prefix)`           | Prefix routes in a router.                             |
| `.tag(...tags)`             | Tag routes for OpenAPI.                                |
| `.router(router)`           | Apply options to a router.                             |
| `.lazy(loader)`             | Apply options to a lazy router.                        |

## See also

* [`makeEffectORPC`](/effect-v4/reference/make-effect-orpc)
* [`EffectBuilder`](/effect-v4/reference/effect-builder)