# `ExMCP.Server.StdioServer`
[🔗](https://github.com/azmaveth/ex_mcp/blob/v1.0.0/lib/ex_mcp/server/stdio_server.ex#L1)

STDIO transport server for MCP protocol.

This server reads from stdin and writes to stdout, making it suitable
for command-line tools and scripting environments.

## Important: STDIO Transport Requirements

The MCP STDIO transport requires that ONLY JSON-RPC messages appear on stdout.
All other output (logs, debug messages, etc.) MUST go to stderr to avoid
contaminating the protocol stream.

## Handling Startup Output

This module implements several strategies to handle startup output from Mix.install
and other sources:

1. **Automatic logging suppression** - Configures all loggers to emergency level
2. **Startup delay** - Waits before reading stdin (configurable via `:stdio_startup_delay`)
3. **Graceful non-JSON handling** - Ignores non-JSON lines instead of sending errors

## Configuration

For scripts using Mix.install, add this before calling Mix.install:

    # Configure STDIO mode and startup delay
    Application.put_env(:ex_mcp, :stdio_mode, true)
    Application.put_env(:ex_mcp, :stdio_startup_delay, 500)  # ms

    # Suppress all logging for clean STDIO JSON-RPC
    System.put_env("ELIXIR_LOG_LEVEL", "emergency")

## Usage

    defmodule MyStdioServer do
      use ExMCP.Server.Handler
      use ExMCP.Server.DSL, name: "my-stdio-server", version: "1.0.0"

      tool "hello", "Says hello" do
        param :name, :string, required: true
        run fn %{name: name}, state -> {:ok, "Hello, #{name}!", state} end
      end
    end

    # Start with STDIO transport
    MyStdioServer.start_link(transport: :stdio)

# `child_spec`

Returns a specification to start this module under a supervisor.

See `Supervisor`.

# `start_link`

Starts the STDIO server.

## Options

* `:module` - The handler module implementing server callbacks
* `:max_request_ids` - Maximum number of distinct client request IDs retained
  for the lifetime of this stdio server process (default: `10_000`)
* Other options are passed to GenServer.start_link

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*Consult [api-reference.md](api-reference.md) for complete listing*