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

# Introduction

> One controlled path from your applications and agents to every service they depend on.

Fused connects your applications and AI agents to internal and external APIs through one controlled runtime. It handles provider credentials, access control, retries, pagination, and execution records so you can focus on what your software does.

Use a **typed SDK**, call the **REST API**, or connect an agent through an **MCP server**. All three use the same Engine, with provider credentials kept out of your application code and agent context.

## How it works

<CardGroup cols={2}>
  <Card title="Registry" icon="cloud">
    A catalogue of versioned service contracts that describe APIs and how to connect to them.
  </Card>

  <Card title="Engine" icon="server">
    Your workspace runtime, hosted or self-hosted. It checks access, resolves credentials, calls providers, and records each execution.
  </Card>
</CardGroup>

Your [workspace](/docs/workspace/enable-a-service) defines which services are available. Each SDK or MCP exposes the operations its caller needs, and [buckets](/docs/bucket/store-credentials) hold the provider credentials used for those calls.

## Get started

First, [get an Engine running](/docs/deploy-an-engine). Then choose what you want to build:

<CardGroup cols={2}>
  <Card title="Build an SDK" icon="cube" href="/docs/quickstart">
    Install the CLI, select operations, and make your first call from a typed package.
  </Card>

  <Card title="Deploy an MCP server" icon="robot" href="/docs/mcp/deploy-a-server">
    Give an agent scoped access to operations across your services.
  </Card>
</CardGroup>

Prefer HTTP without a generated package? Follow the [direct API setup](/docs/app/build-an-sdk#skip-the-package).