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Sep 18, 2025
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docs: document stateless mode and custom transports #485

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32 changes: 26 additions & 6 deletions docs/protocol.md
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Original file line number Diff line number Diff line change
Expand Up @@ -182,15 +182,35 @@ the server using the streamable transport protocol.

#### Stateless Mode

<!-- TODO -->

#### Sessionless mode

<!-- TODO -->
The streamable server supports a _stateless mode_ by setting
[`StreamableHTTPOptions.Stateless`](https://pkg.go.dev/github.com/modelcontextprotocol/go-sdk/mcp#StreamableHTTPOptions.Stateless),
which is where the server does not perform any validation of the session id,
and uses a temporary session to handle requests. In this mode, it is impossible
for the server to make client requests, as there is no way for the client's
response to reach the session.

However, it is still possible for the server to access the `ServerSession.ID`
to see the logical session

> [!WARNING]
> Stateless mode is not directly discussed in the spec, and is still being
> defined. See modelcontextprotocol/modelcontextprotocol#1364,
> modelcontextprotocol/modelcontextprotocol#1372, or
> modelcontextprotocol/modelcontextprotocol#11442 for potential refinements.

_See [examples/server/distributed](../examples/server/distributed/main.go) for
an example using statless mode to implement a server distributed across
multiple processes._

### Custom transports

<!-- TODO -->
The SDK supports [custom
transports](https://modelcontextprotocol.io/specification/2025-06-18/basic/transports#custom-transports)
by implementing the
[`Transport`](https://pkg.go.dev/github.com/modelcontextprotocol/go-sdk/mcp#Transport)
interface: a logical bidirectional stream of JSON-RPC messages.

_Full example: [examples/server/custom-transport](../examples/server/custom-transport/main.go)._

### Concurrency

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32 changes: 26 additions & 6 deletions internal/docs/protocol.src.md
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Original file line number Diff line number Diff line change
Expand Up @@ -114,15 +114,35 @@ the server using the streamable transport protocol.

#### Stateless Mode

<!-- TODO -->

#### Sessionless mode

<!-- TODO -->
The streamable server supports a _stateless mode_ by setting
[`StreamableHTTPOptions.Stateless`](https://pkg.go.dev/github.com/modelcontextprotocol/go-sdk/mcp#StreamableHTTPOptions.Stateless),
which is where the server does not perform any validation of the session id,
and uses a temporary session to handle requests. In this mode, it is impossible
for the server to make client requests, as there is no way for the client's
response to reach the session.

However, it is still possible for the server to access the `ServerSession.ID`
to see the logical session

> [!WARNING]
> Stateless mode is not directly discussed in the spec, and is still being
> defined. See modelcontextprotocol/modelcontextprotocol#1364,
> modelcontextprotocol/modelcontextprotocol#1372, or
> modelcontextprotocol/modelcontextprotocol#11442 for potential refinements.

_See [examples/server/distributed](../examples/server/distributed/main.go) for
an example using statless mode to implement a server distributed across
multiple processes._

### Custom transports

<!-- TODO -->
The SDK supports [custom
transports](https://modelcontextprotocol.io/specification/2025-06-18/basic/transports#custom-transports)
by implementing the
[`Transport`](https://pkg.go.dev/github.com/modelcontextprotocol/go-sdk/mcp#Transport)
interface: a logical bidirectional stream of JSON-RPC messages.

_Full example: [examples/server/custom-transport](../examples/server/custom-transport/main.go)._

### Concurrency

Expand Down
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