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Streamable http MCP server handshaking failed #5208

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#5542
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Streamable http MCP server handshaking failed#5208
#5542
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gpeal
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bugSomething isn't workingmcpIssues related to the use of model context protocol (MCP) servers

Description

@ouyangjunfei
ouyangjunfei
opened on Oct 15, 2025

What version of Codex is running?

codex-cli 0.46.0

Which model were you using?

qwen3-coder-plus

What platform is your computer?

Darwin 23.5.0 arm64 arm

What steps can reproduce the bug?

  1. Add a custom mcp server config（url just for example cause it's deployed in our net)
[mcp_servers.custom]
url = "https://xxx.yyy.com/mcp"

2 Open codex

codex
  1. Wait
    CLI shows error :

MCP client for custom failed to start: handshaking with MCP server failed: Send message error Transport
[rmcp::transport::worker::WorkerTransport<rmcp::transport::streamable_http_client::StreamableHttpClientWorker<reqwest::a
sync_impl::client::Client>>] error: Transport channel closed, when send initialized notification

And no tools:

Image

What is the expected behavior?

No errors for mcp servers, and I can see tools.

Same MCP Server URL for claude code works fine

Image

What do you see instead?

No response

Additional information

No response

Activity

  1. ouyangjunfei
    added
    bugSomething isn't working
    on Oct 15, 2025
  2. github-actions
    added
    mcpIssues related to the use of model context protocol (MCP) servers
    on Oct 15, 2025

  3. github-actions commented on Oct 15, 2025

    @github-actions
    github-actionsBot
    on Oct 15, 2025 – with GitHub Actions
    Contributor

    Potential duplicates detected. Please review them and close your issue if it is a duplicate.

    Powered by Codex Action

  4. moxi000 commented on Oct 17, 2025

    @moxi000
    moxi000
    on Oct 17, 2025

    same problem, however correctly work in cursor and claudecode

  5. gpeal commented on Oct 17, 2025

    @gpeal
    gpeal
    on Oct 17, 2025
    Contributor

    Can you reproduce this issue with any other MCP servers? Does your MCP server support dynamic client registration? Does it require anything else like custom headers?

  6. gpeal
    self-assigned this
    on Oct 17, 2025

  7. moxi000 commented on Oct 18, 2025

    @moxi000
    moxi000
    on Oct 18, 2025

    Can you reproduce this issue with any other MCP servers? Does your MCP server support dynamic client registration? Does it require anything else like custom headers?

    @gpeal Yes, I found that others have similar feedback. We use different MCP servers. To make it easier for you to test, I provide you with an MCP link with an authorization code. In cursor or claudecode, you can directly add the URL to obtain the tool list and call it. It will only report an error in codex.

    https://mcp.allflow.cn/message?token=uwP1eH5SoKaA2kRGGKjk9GCbbkvtk06RUVUtNbZH

  8. hwait commented on Oct 18, 2025

    @hwait
    hwait
    on Oct 18, 2025

    I can confirm the issue with Linear:

    model = "gpt-5-codex"
experimental_use_rmcp_client = true

[mcp_servers]
[mcp_servers.linear]
url = "https://mcp.linear.app/mcp"

    It worked well couple of days ago.

  9. moxi000 commented on Oct 18, 2025

    @moxi000
    moxi000
    on Oct 18, 2025

    I can confirm the issue with Linear:

    model = "gpt-5-codex"
experimental_use_rmcp_client = true

[mcp_servers]
[mcp_servers.linear]
url = "https://mcp.linear.app/mcp"

    It worked well couple of days ago.
    @hwait Can you test with this link? https://mcp.allflow.cn/message?token=uwP1eH5SoKaA2kRGGKjk9GCbbkvtk06RUVUtNbZH

    I still can’t use it normally.

  10. hwait commented on Oct 18, 2025

    @hwait
    hwait
    on Oct 18, 2025

    I updated codex to v0.47.0 but unfortunately it did not help.
    @moxi000 your server gives me

    MCP client for `allflow` failed to start: handshaking with MCP server failed: Send message error Transport
[rmcp::transport::worker::WorkerTransport<rmcp::transport::streamable_http_client::StreamableHttpClientWorker<reqwest::async
_impl::client::Client>>] error: Transport channel closed, when send initialized notification

  11. dominicdill commented on Oct 22, 2025

    @dominicdill
    dominicdill
    on Oct 22, 2025
    Image

    MCP client for langchain failed to start: handshaking with MCP server failed: Send message error Transport
    [rmcp::transport::worker::WorkerTransport<rmcp::transport::streamable_http_client::StreamableHttpClientWorkerreqwest::async_impl::client::Client>] error: Client error: HTTP status server error (500 Internal
    Server Error) for url (https://docs.langchain.com/mcp), when send initialize request

    config.toml:

    Image

    Is this a related issue? Have I done something wrong?

  12. gpeal commented on Oct 22, 2025

    @gpeal
    gpeal
    on Oct 22, 2025
    Contributor
    Image MCP client for `langchain` failed to start: handshaking with MCP server failed: Send message error Transport [rmcp::transport::worker::WorkerTransport] error: Client error: HTTP status server error (500 Internal Server Error) for url (https://docs.langchain.com/mcp), when send initialize request

    config.toml:

    Image Is this a related issue? Have I done something wrong?

    Sounds like there was an issue on their end, I just tried and it worked

    Image

  13. moxi000 commented on Oct 22, 2025

    @moxi000
    moxi000
    on Oct 22, 2025

    @gpeal Can you try with my link？https://mcp.allflow.cn/message?token=uwP1eH5SoKaA2kRGGKjk9GCbbkvtk06RUVUtNbZH

  14. rafaelquintanilha commented on Oct 22, 2025

    @rafaelquintanilha
    rafaelquintanilha
    on Oct 22, 2025

    I had the same issue. Fixed by doing the following:

    codex mcp remove linear
codex mcp add --url https://mcp.linear.app/mcp linear
codex mcp login linear -c experimental_use_rmcp_client=true

# Confirm it's working
codex mcp get linear

  15. gpeal commented on Oct 22, 2025

    @gpeal
    gpeal
    on Oct 22, 2025
    Contributor

    @gpeal Can you try with my link？https://mcp.allflow.cn/message?token=uwP1eH5SoKaA2kRGGKjk9GCbbkvtk06RUVUtNbZH

    I do see the issue with that mcp server. I'll investigate separately. Feel free to take a look as well. It's all open source.

  16. gpeal commented on Oct 22, 2025

    @gpeal
    gpeal
    on Oct 22, 2025
    Contributor

    @moxi000 your issue will be resolved by modelcontextprotocol/rust-sdk#497

  17. moxi000 commented on Oct 23, 2025

    @moxi000
    moxi000
    on Oct 23, 2025

    @moxi000 your issue will be resolved by modelcontextprotocol/rust-sdk#497

    Thanks

  18. hwait commented on Oct 23, 2025

    @hwait
    hwait
    on Oct 23, 2025

    I had the same issue. Fixed by doing the following:

    codex mcp remove linear
codex mcp add --url https://mcp.linear.app/mcp linear
codex mcp login linear -c experimental_use_rmcp_client=true

# Confirm it's working
codex mcp get linear

    Thank you, Rafael, worked well!

  19. gpeal commented on Oct 23, 2025

    @gpeal
    gpeal
    on Oct 23, 2025
    Contributor

    I'm going to close this out now because the allflow issue was fixed by #5542

    Please open new issues for anything that happens in 0.48 or later

  20. gpeal
    closed this as completedon Oct 23, 2025
  21. gpeal
    added a commit that references this issue on Oct 24, 2025

    [MCP] Update rmcp to 0.8.3 (#5542)

    abccd3e
  22. JeffCarpenter
    added a commit that references this issue on Oct 28, 2025

    [MCP] Update rmcp to 0.8.3 (openai#5542)

    7e76388
  23. DioNanos
    added a commit that references this issue on Nov 10, 2025

    [MCP] Update rmcp to 0.8.3 (openai#5542)

    3e7cea7
  24. willy3087
    added a commit that references this issue on Nov 14, 2025

    [MCP] Update rmcp to 0.8.3 (openai#5542)

    37278b6
  25. takumi-earth
    added a commit that references this issue on Dec 2, 2025

    [MCP] Update rmcp to 0.8.3 (openai#5542)

    621c054
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