How should the env parameter be passed in stdio mode?

[Apple-Blossom23]

from fastmcp import Client

client = Client(
"fast_mcp_server.py",
env={"API_KEY": "secret", "DEBUG": "true"}
)

TypeError: Client.init() got an unexpected keyword argument 'env'

my fastmcp version is 2.12.3

[KaliszS]

Hello @Fs1114508. env argument is an attribute of StdioTransport class, not Client. Example below should work:

from fastmcp import Client
from fastmcp.client.transports import StdioTransport

transport = StdioTransport(
    command="python", 
    args=["fast_mcp_server.py"],
    env={"API_KEY": "secret", "DEBUG": "true"}
)

client = Client(transport)

[Apple-Blossom23]

Thank you, I understand.

…

------------------ Original ------------------ From: Sebastian Kalisz ***@***.***> Date: Fri,Sep 19,2025 7:11 PM To: jlowin/fastmcp ***@***.***> Cc: Fs1114508 ***@***.***>, Mention ***@***.***> Subject: Re: [jlowin/fastmcp] How should the env parameter be passed in stdiomode? (Discussion #1855) Hello @Fs1114508. env keyword is an attribute of StdioTransport class, not Client. Example below should work: from fastmcp import Client from fastmcp.client.transports import StdioTransport transport = StdioTransport( command="python", args=["fast_mcp_server.py"], env={"API_KEY": "secret", "DEBUG": "true"} ) client = Client(transport) — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you were mentioned.Message ID: ***@***.***>

[KaliszS]

Please, remember, there is an option to choose the correct answer and resolves the question, so it won't float around as unanswered ;)