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[GH-ISSUE #4062] [langsmith]: LangSmith Remote MCP Doesn't Work on Cursor #2777

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opened 2026-06-05 17:26:44 -04:00 by yindo · 3 comments
yindo commented 2026-06-05 17:26:44 -04:00
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Originally created by @samuel-poon on GitHub (May 18, 2026).
Original GitHub issue: https://github.com/langchain-ai/docs/issues/4062

Type of issue

issue / bug

Language

N/A

Description

I followed the instructions for LangSmith Remote MCP for Cursor, but encountered Error - Show Output. When I look into my logs, I see the following:

2026-05-18 22:00:47.278 [info] [V2] Handling DeleteClient action, reason: server_disabled
2026-05-18 22:00:47.529 [info] [V2] Handling CreateClient action
2026-05-18 22:00:47.529 [info] [V2 FSM] connection:connect_start: conn=idle,auth=unknown -> conn=connecting,auth=unknown
2026-05-18 22:00:48.787 [info] MCP OAuth provider initialized
2026-05-18 22:00:48.846 [warning] MCP HTTP exchange completed
2026-05-18 22:00:48.976 [info] MCP HTTP exchange completed
2026-05-18 22:00:49.033 [info] MCP HTTP exchange completed
2026-05-18 22:00:49.310 [info] Registration lock held by sibling — waiting
2026-05-18 22:00:52.781 [info] Registration lock released — sibling did not complete, proceeding with own registration
2026-05-18 22:00:52.782 [info] No stored client information found
2026-05-18 22:00:52.855 [warning] MCP HTTP exchange completed
2026-05-18 22:00:52.857 [warning] Transient error connecting to streamableHttp server: redirect_uri must be http loopback or https to a domain host
2026-05-18 22:00:52.859 [warning] Connection failed: redirect_uri must be http loopback or https to a domain host
2026-05-18 22:00:52.859 [warning] [V2 FSM] connection:connect_failure: conn=connecting,auth=unknown -> conn=failed,auth=unknown
2026-05-18 22:00:52.859 [info] CreateClient completed, connected: false, statusType: error

I used to use the hosted LangSmith MCP sever at https://langsmith-mcp-server.onrender.com/mcp with no problems but it is now deprecated.

Originally created by @samuel-poon on GitHub (May 18, 2026). Original GitHub issue: https://github.com/langchain-ai/docs/issues/4062 ### Type of issue issue / bug ### Language N/A ### Description I followed the instructions for LangSmith Remote MCP for Cursor, but encountered _Error - Show Output_. When I look into my logs, I see the following: ```bash 2026-05-18 22:00:47.278 [info] [V2] Handling DeleteClient action, reason: server_disabled 2026-05-18 22:00:47.529 [info] [V2] Handling CreateClient action 2026-05-18 22:00:47.529 [info] [V2 FSM] connection:connect_start: conn=idle,auth=unknown -> conn=connecting,auth=unknown 2026-05-18 22:00:48.787 [info] MCP OAuth provider initialized 2026-05-18 22:00:48.846 [warning] MCP HTTP exchange completed 2026-05-18 22:00:48.976 [info] MCP HTTP exchange completed 2026-05-18 22:00:49.033 [info] MCP HTTP exchange completed 2026-05-18 22:00:49.310 [info] Registration lock held by sibling — waiting 2026-05-18 22:00:52.781 [info] Registration lock released — sibling did not complete, proceeding with own registration 2026-05-18 22:00:52.782 [info] No stored client information found 2026-05-18 22:00:52.855 [warning] MCP HTTP exchange completed 2026-05-18 22:00:52.857 [warning] Transient error connecting to streamableHttp server: redirect_uri must be http loopback or https to a domain host 2026-05-18 22:00:52.859 [warning] Connection failed: redirect_uri must be http loopback or https to a domain host 2026-05-18 22:00:52.859 [warning] [V2 FSM] connection:connect_failure: conn=connecting,auth=unknown -> conn=failed,auth=unknown 2026-05-18 22:00:52.859 [info] CreateClient completed, connected: false, statusType: error ``` I used to use the hosted LangSmith MCP sever at `https://langsmith-mcp-server.onrender.com/mcp` with no problems but it is now deprecated.
yindo added the langsmithexternal labels 2026-06-05 17:26:44 -04:00
yindo commented 2026-06-05 17:26:45 -04:00
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@alexkappa commented on GitHub (May 25, 2026):

We're also experiencing this same issue.

<!-- gh-comment-id:4533681810 --> @alexkappa commented on GitHub (May 25, 2026): We're also experiencing this same issue.
yindo commented 2026-06-05 17:26:45 -04:00
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@razvanbretoiu commented on GitHub (Jun 4, 2026):

same. We are receiving the same issue. Tried with GCP EU region and GCP US region.

<!-- gh-comment-id:4621750578 --> @razvanbretoiu commented on GitHub (Jun 4, 2026): same. We are receiving the same issue. Tried with GCP EU region and GCP US region.
yindo commented 2026-06-05 17:26:45 -04:00
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@jamesford67 commented on GitHub (Jun 5, 2026):

I have also run into the same issue.

It looks like Cursor's native remote MCP OAuth uses a custom URI scheme that LangSmith's policy blocks. Would it be possible to documenting a workaround for this? LangSmith accepting the custom scheme would also fix this (cursor uses a redirect URI of cursor://anysphere.cursor-mcp/oauth/callback which can't be changed), but I understand if that isn't possible.

<!-- gh-comment-id:4635449541 --> @jamesford67 commented on GitHub (Jun 5, 2026): I have also run into the same issue. It looks like Cursor's native remote MCP OAuth uses a custom URI scheme that LangSmith's policy blocks. Would it be possible to documenting a workaround for this? LangSmith accepting the custom scheme would also fix this (cursor uses a redirect URI of cursor://anysphere.cursor-mcp/oauth/callback which can't be changed), but I understand if that isn't possible.
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Reference: langchain-ai/docs#2777
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