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

# Flow diagrams

> Visualize Fentaris request routing and lifecycle.

Use these diagrams to understand how requests move through Fentaris. Each diagram maps to an operational moment: initialization, discovery, and tool calls. This is helpful when you want to explain the system to a new team member or debug a request path.

If you are building a custom transport or middleware chain, keep this page open as a reference.

## Initialization flow

```mermaid theme={"theme":{"light":"github-light","dark":"github-dark"}}
sequenceDiagram
  participant Client
  participant Proxy
  participant Session

  Client->>Proxy: POST /mcp (initialize)
  Proxy->>Session: create Streamable HTTP session
  Session-->>Client: session id
```

During initialization the proxy creates a session and attaches the MCP SDK server transport. This is the point where `name` and `version` are announced to the client.

## Tool discovery flow

```mermaid theme={"theme":{"light":"github-light","dark":"github-dark"}}
sequenceDiagram
  participant Client
  participant Proxy
  participant ServerA
  participant ServerB

  Client->>Proxy: listTools
  Proxy->>ServerA: listTools
  Proxy->>ServerB: listTools
  Proxy-->>Client: merged tools (prefixed names)
```

Tool discovery is where `onListTools` filters run. Use this to hide internal tools or to expose only the subset allowed for the current user.

## Tool call flow with middleware

```mermaid theme={"theme":{"light":"github-light","dark":"github-dark"}}
flowchart LR
  Client --> Proxy
  Proxy --> Hooks
  Hooks --> Middleware
  Middleware --> Server
  Server --> Middleware
  Middleware --> Client
```

Hooks run first and can short-circuit a call. Middleware runs next and can enforce policy, inject guidance, and augment logs. The server is only invoked when middleware allows it.

## Where to go next

* For policy and access control, see [Middleware](/guides/middleware).
* For targeted audits, see [Hooks](/guides/hooks).
* For transport details, see [Transports](/core/transports).