modelcontextprotocol / modelcontextprotocol/typescript-sdk
MCP SDK Can not handle the MCP Servers with subpath
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- Dominant language
- TypeScript
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Description
Issue:
Clients (Inspector/Cherry Studio) fail to connect when MCP Server uses a subpath (e.g., http://domain.com/subpath/sse). Root paths (http://domain.com/) work normally.
Reproduce:
- Start MCP Server at
http://domain.com/subpath/sse - Client connection fails with error:
Error POSTing to endpoint (HTTP 503): no healthy upstream
Cause:
In sse.ts#L146, new URL() discards the subpath from the server URL. Example:
Request to /messages/ becomes http://domain.com/messages/ instead of http://domain.com/subpath/messages/.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reading src/client/sse.ts around line 146 and trace how the server URL is used to construct the messages request. Reproduce the connection against a server mounted at a subpath, then verify that the request retains the subpath while root-path connections continue to work.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- typescript
- Domain
- api
- Issue type
- Bug
- Difficulty
- 2/5
- Estimated time
- 1-3 hours
- Activity status
- Quiet
- Clarity
- Clearly specified
- Newbie friendliness
- 72/100