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claude-code - 💡(How to fix) Fix [BUG] VS Code extension cannot connect to SSE MCP servers that require POST method [1 participants]

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anthropics/claude-code#54131•Fetched 2026-04-28 06:38:24
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Error Message

Claude Code VS Code extension with "SSE error: Non-200 status code (405)"

Code Example

Claude Code VS Code extension with "SSE error: Non-200 status code (405)"
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Preflight Checklist

  • I have searched existing issues and this hasn't been reported yet
  • This is a single bug report (please file separate reports for different bugs)
  • I am using the latest version of Claude Code

What's Wrong?

Some SSE-based MCP servers require POST requests instead of GET These servers return HTTP 405 (Method Not Allowed) with Allow: POST header The same SSE MCP server configuration works fine in: Claude CLI (when used by skills) Cline VS Code extension Claude Desktop app But fails in Claude Code VS Code extension with "SSE error: Non-200 status code (405)" Claude Code's VS Code extension should support POST-based SSE connections like other MCP clients do

Actual behavior: Connection fails with 405 error, making these enterprise SSE MCP endpoints unusable in the VS Code extension.

This affects any organization deploying SSE-based MCP servers that follow the POST pattern.

What Should Happen?

Expected behavior: SSE MCP servers that use POST should connect successfully, as they do in other Claude clients.

Error Messages/Logs

Claude Code VS Code extension with "SSE error: Non-200 status code (405)"

Steps to Reproduce

Configure an SSE MCP server in ~/.claude.json that requires POST method:

{ "mcpServers": { "test-sse-server": { "type": "sse", "url": "https://example.com/mcp", "headers": { "Authorization": "Bearer <token>" } } } } Ensure the SSE endpoint at https://example.com/mcp:

Returns HTTP 401/405 on GET requests Returns HTTP 405 with Allow: POST header when using GET with auth Accepts POST requests for SSE connection Reload VS Code window ("Developer: Reload Window")

Check MCP server status in Claude Code chat interface

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

No response

Claude Code Version

2.1.120

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

No response

extent analysis

TL;DR

Modify the Claude Code VS Code extension to support POST requests for SSE connections by updating the request method in the SSE client implementation.

Guidance

  • Investigate the SSE client implementation in the Claude Code VS Code extension to identify where the request method is set to GET, and consider updating it to support POST requests.
  • Verify that the SSE endpoint returns a 200 status code when a POST request is sent with the correct authentication headers.
  • Check the Allow header in the 405 response to confirm that the server expects a POST request.
  • Consider adding a configuration option to the Claude Code VS Code extension to allow users to specify the request method for SSE connections.

Example

No code snippet is provided as the issue does not include the relevant code, but the fix would involve updating the SSE client implementation to use the POST method, for example:

// hypothetical example, not based on actual code
const response = await fetch(sseUrl, {
  method: 'POST', // update the request method to POST
  headers: {
    Authorization: 'Bearer <token>',
  },
});

Notes

The fix may require updates to the Claude Code VS Code extension's SSE client implementation, and may involve adding configuration options or modifying the request headers.

Recommendation

Apply a workaround by modifying the Claude Code VS Code extension to support POST requests for SSE connections, as this is a specific fix for the reported issue and does not require upgrading to a different version.

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