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

# Architecture Overview

> How Relayer Kits relate to each other and to your application

Relayer is organized into Kits. Each Kit covers a distinct domain and exposes a set of REST endpoints under the `/v1` prefix. This page shows how the Kits relate to each other and to your application.

## Kit Structure

```mermaid theme={null}
graph TB
    subgraph "Your Application"
        APP[Your Backend / Dashboard]
        FE[Your Frontend]
    end

    subgraph "Relayer API /v1"
        SI[Signing Kit<br/>/v1/signing/*]
        AG[Agent Kit<br/>/v1/agents/*]
        PA[Payout Kit<br/>/v1/payout/*]
        WI[Widget Kit<br/>/v1/action/builders/* + /execute/*]
    end

    APP -->|Bearer JWT or ApiKey| SI
    APP -->|Bearer JWT or ApiKey| AG
    APP -->|Bearer JWT or ApiKey| PA
    APP -->|Bearer JWT or ApiKey| WI
    FE -->|npm install @relayer-fi/widgets| WI
```

## Kit Responsibilities

| Kit            | Prefix                                                    | What It Does                                                                            |
| -------------- | --------------------------------------------------------- | --------------------------------------------------------------------------------------- |
| **Signing**    | `/v1/signing`, `/v1/transactions`                         | Self-custodial wallets, transaction prepare/confirm, passkey signing, approval policies |
| **Agent Kit**  | `/v1/agents`                                              | Budget-enforced AI agents that can sign transactions and pay for x402 resources         |
| **Payout**     | `/v1/payout`, `/v1/orders`                                | Fiat on/off-ramp, recipient management, virtual accounts, payment settlement            |
| **Widget Kit** | `/v1/action/builders`, `/v1/action/execute`, npm packages | Embeddable widgets for canonical protocols (swap, transfer, bridge)                     |

## Request Flow

Every API request follows the same pattern:

```mermaid theme={null}
sequenceDiagram
    participant App as Your App
    participant API as Relayer API
    participant Kit as Kit Module

    App->>API: POST /v1/{kit}/{resource}<br/>Authorization: ApiKey rk_...
    API->>API: Validate API key + module + permissions
    API->>Kit: Route to Kit module
    Kit-->>API: Result
    API-->>App: { success, data, statusCode, ... }
```

## Authentication Model

Every request authenticates with an API key in the `Authorization` header:

```
Authorization: ApiKey rk_client_key_v1_your_key_here
```

The API key identifies the integrator (your workspace) and determines which Kits and resources are accessible based on the workspace's active modules and the caller's role.

Some surfaces also accept a session JWT (`Authorization: Bearer <jwt>`) for browser-side callers from the Relayer dashboard, and the Agent Kit accepts an HMAC-signed `X-Agent-Auth` header for runtime calls from the agent SDK. See [Authentication](/get-started/authentication) for the full matrix.

## Environments

| Environment | Base URL                        | Use                     |
| ----------- | ------------------------------- | ----------------------- |
| Sandbox     | `https://testnet.relayer.fi/v1` | Development and testing |
| Production  | `https://api.relayer.fi/v1`     | Live operations         |

All Kit endpoints and authentication patterns are identical across environments.