difference between python-sdk and ruby-sdk in a fast-agent

[dmlond]

Describe the bug
I am trying to use a ruby-sdk stdio server in a fastagent agent. I have a python-sdk implementation and a ruby-sdk implementation. Both can be run at the commandline and I can send ping jsonrpc requests to them. Only the python implementation works in fastagent.

To Reproduce
Steps to reproduce the behavior:

1. install python and ruby
2. create mcp directory
3. add pcalc.py
4. add rcalc.rb
5. Initialize a fast-agent and configure it to use stdio rcalc and pcalc
6. run fast-agent go --servers pcalc
7. run fast-agent go --servers rcalc
8. create Expected behaviorA clear and concise description of what you expected to happen.LogsIf applicable, add logs to help explain your problem.

I would expect both to work, and the fast-agent to allow me to use both in the same way

Additional context
Add any other context about the problem here.

rcalc

require 'mcp'
require 'mcp/server/transports/stdio_transport'

# Create a simple tool
class ExampleTool < MCP::Tool
  description 'A simple example tool that adds two numbers'
  input_schema(
    properties: {
      a: { type: 'number' },
      b: { type: 'number' }
    },
    required: %w[a b]
  )

  class << self
    def call(a:, b:)
      MCP::Tool::Response.new([{
                                type: 'text',
                                text: "The sum of #{a} and #{b} is #{a + b}"
                              }])
    end
  end
end

# Set up the server
server = MCP::Server.new(
  name: 'example_server',
  version: '1.0.0',
  tools: [ExampleTool]
)

# Create and start the transport
transport = MCP::Server::Transports::StdioTransport.new(server)
transport.open

pcalc

require 'mcp'
require 'mcp/server/transports/stdio_transport'

# Create a simple tool
class ExampleTool < MCP::Tool
  description 'A simple example tool that adds two numbers'
  input_schema(
    properties: {
      a: { type: 'number' },
      b: { type: 'number' }
    },
    required: %w[a b]
  )

  class << self
    def call(a:, b:)
      MCP::Tool::Response.new([{
                                type: 'text',
                                text: "The sum of #{a} and #{b} is #{a + b}"
                              }])
    end
  end
end

# Set up the server
server = MCP::Server.new(
  name: 'example_server',
  version: '1.0.0',
  tools: [ExampleTool]
)

# Create and start the transport
transport = MCP::Server::Transports::StdioTransport.new(server)
transport.open

When fast-agent go --servers rcalc runs, it experiences an error on initialization and exits
$ fast-agent go --servers rcalc
[fast_agent.mcp.mcp_agent_client_session] send_request failed: Connection closed
[fast_agent.mcp.mcp_connection_manager] rcalc: Lifecycle task encountered an error: unhandled errors in a TaskGroup (1
sub-exception)

MCP Server Startup Error:
MCP Server: 'rcalc': Failed to initialize - see details. Check fastagent.config.yaml?

Details:
McpError: Connection closed

There was an error starting up the MCP Server.

[dmlond]

I solved this issue. It was unrelated to the mcp server.