---
title: "a4-server"
description: "Run your Arete projections as a WebSocket server."
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---

`a4-server` is a Rust crate that lets you run your compiled stack as a standalone WebSocket server. It connects to a Yellowstone gRPC endpoint, processes Solana data through your projections, and streams the results to connected clients.

## Prerequisites

To run a stack with `a4-server`, you need:

| Requirement                   | Description                                                                                                                                          |
| ----------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Yellowstone gRPC Endpoint** | A URL to a Solana node running the [Yellowstone Geyser plugin](https://github.com/rpcpool/yellowstone-grpc). This is your source of blockchain data. |
| **X-Token**                   | Authentication token for your Yellowstone provider (most providers require this).                                                                    |
| **Rust 1.75+**                | Required to build the server binary.                                                                                                                 |
| **A compiled stack**          | Your stack crate with the `#[arete(...)]` macro, which generates a `spec()` function.                                                                |

:::caution[Yellowstone Access Required]
You must have access to a Yellowstone gRPC endpoint. Options include:

- Running your own Solana validator with the Yellowstone Geyser plugin
- Using a provider like Triton, Helius, or similar that offers Yellowstone gRPC
  :::

## Environment Variables

`a4-server` reads configuration from environment variables:

| Variable               | Required | Description                           |
| ---------------------- | -------- | ------------------------------------- |
| `YELLOWSTONE_ENDPOINT` | Yes      | Your Yellowstone gRPC endpoint URL    |
| `YELLOWSTONE_X_TOKEN`  | Usually  | Authentication token for the endpoint |

## When to Use a4-server

**Use a4-server when:**

- Developing and testing stacks locally
- Running a single stack in your own infrastructure
- You need full control over the server deployment
- You already have Yellowstone gRPC access

**Consider Arete Cloud when:**

- You need multi-stack orchestration
- You want managed Yellowstone infrastructure
- You need built-in authentication and API keys
- You prefer zero-config deployment