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

# Configuration & environment

> Server bind address and port, the Content-Type requirement, request limits, version, and what is (and isn't) configurable via environment.

Euca's server is deliberately simple to run. This page lists the operational knobs, grounded in code.

## Server

| Setting           | Value              | Notes                                                                                                                                    |
| ----------------- | ------------------ | ---------------------------------------------------------------------------------------------------------------------------------------- |
| **Bind address**  | `127.0.0.1`        | Localhost only — no remote binding by design                                                                                             |
| **Port**          | `3917` (fixed)     | The headless host (`euca-studio --headless`) binds `3917`; the CLI and OpenAPI default to it too                                         |
| **Content-Type**  | `application/json` | Required on all POST requests                                                                                                            |
| **`/step` limit** | `10,000` ticks     | Per call (clamped)                                                                                                                       |
| **Auth**          | none by default    | Unauthenticated by default (no global gate); **opt-in Ed25519** login + per-agent ownership — see [Hosting](/systems/hosting-deployment) |
| **Version**       | `1.1.0`            | Workspace version, Rust edition 2024                                                                                                     |

```bash theme={null}
cargo run -p euca-studio -- --headless
```

## Environment variables

* **There is no `EUCA_URL`.** Clients take a base URL directly — the CLI via `--server`
  (default `http://localhost:3917`), HTTP clients via their own config.
* **Asset-generation keys** — the [asset pipeline](/systems/asset-generation) reads provider API keys
  from the environment (`TRIPO_API_KEY`, `MESHY_API_KEY`, …). None ship by default; an `.env.example`
  documents the shape.
* **`ANTHROPIC_API_KEY`** — used only by the benchmark crate's optional LLM grading, not the engine.

## Rendering options

Rendering features like **MetalFX** are **runtime renderer options** (`renderer.enable_metalfx(true)`),
not compile-time feature flags — there's no server-level flag to toggle them. See
[Engine internals](/concepts/engine-internals) for which render features are on by default vs. opt-in.

## What the headless host registers

The headless host (`euca-studio --headless`) boots the engine-level resources and runs the selected
project's **full game logic** (`game.step`) each tick — the same per-tick behavior as the windowed host,
just with no window or GPU. What it does **not** provide is anything that needs hardware or a host-supplied
resource: there is no GPU/camera, no audio device, and it doesn't register a
`TemplateRegistry`/`PrefabRegistry`, an input `ActionMap`, or a Lua `ScriptEngine` unless the project's game
does. So those endpoints no-op, error, or require a render host (see
[Troubleshooting](/reference/troubleshooting)). Register the resources you need in your project's game or
on your own host build.

<Card title="Hosting & deployment" icon="server" href="/systems/hosting-deployment" horizontal>
  Running a server, auth posture, and platform support.
</Card>