Cursor MCP finds tool but report and eror (localhost)

Support Bug Reports
1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

In the latest cursor

Version: 2.3.34VSCode Version: 1.105.1Commit: 643ba67cd252e2888e296dd0cf34a0c5d7625b90Date: 2026-01-10T21:17:10.428ZElectron: 37.7.0Chromium: 138.0.7204.251Node.js: 22.20.0V8: 13.8.258.32-electron.0OS: Linux x64 6.18.2

it finds the tools but then error out with one error. No explanation is given what the error means and the error seems incomplete as well.

] Client error for command Streamable HTTP error: Error POSTing to endpoint:

2026-01-12 22:34:13.501 [info] Handling DeleteClient action
2026-01-12 22:34:13.501 [info] Cleaning up
2026-01-12 22:34:14.029 [info] Handling CreateClient action
2026-01-12 22:34:14.030 [info] Creating streamableHttp transport
2026-01-12 22:34:14.043 [info] Using OAuth scopes: mcp:connect
2026-01-12 22:34:14.043 [info] Connecting to streamableHttp server
2026-01-12 22:34:14.052 [info] No stored tokens found
2026-01-12 22:34:14.068 [info] No stored tokens found
2026-01-12 22:34:14.076 [info] Successfully connected to streamableHttp server
2026-01-12 22:34:14.076 [info] Storing streamableHttp client
2026-01-12 22:34:14.076 [info] CreateClient completed, server stored: true
2026-01-12 22:34:14.085 [info] No stored tokens found
2026-01-12 22:34:14.087 [info] No stored tokens found
2026-01-12 22:34:14.090 [info] Handling ListOfferings action, server stored: true
2026-01-12 22:34:14.091 [info] Connected to streamableHttp server, fetching offerings
2026-01-12 22:34:14.093 [info] No stored tokens found
2026-01-12 22:34:14.099 [info] No stored tokens found
2026-01-12 22:34:14.103 [info] listOfferings: Found 3 tools
2026-01-12 22:34:14.106 [info] No stored tokens found
2026-01-12 22:34:14.109 [error] Client error for command Streamable HTTP error: Error POSTing to endpoint:
2026-01-12 22:34:14.112 [info] listPrompts: Found 1 prompts
2026-01-12 22:34:14.132 [info] No stored tokens found
2026-01-12 22:34:14.138 [info] listResources: Found 1 resources
2026-01-12 22:34:14.139 [info] Found 3 tools, 1 prompts, and 1 resources
2026-01-12 22:34:21.703 [info] Handling ListOfferings action, server stored: true
2026-01-12 22:34:21.704 [info] Connected to streamableHttp server, fetching offerings
2026-01-12 22:34:21.718 [info] No stored tokens found
2026-01-12 22:34:21.739 [info] listOfferings: Found 3 tools
2026-01-12 22:34:21.742 [info] No stored tokens found
2026-01-12 22:34:21.747 [info] listPrompts: Found 1 prompts
2026-01-12 22:34:21.749 [info] No stored tokens found
2026-01-12 22:34:21.756 [info] listResources: Found 1 resources
2026-01-12 22:34:21.756 [info] Found 3 tools, 1 prompts, and 1 resources

Steps to Reproduce

use a localhost streamble http(s) server and add into cursor

Expected Behavior

Load the tools without error

Operating System

Linux

Current Cursor Version (Menu → About Cursor → Copy)

Version: 2.3.34
VSCode Version: 1.105.1
Commit: 643ba67cd252e2888e296dd0cf34a0c5d7625b90
Date: 2026-01-10T21:17:10.428Z
Electron: 37.7.0
Chromium: 138.0.7204.251
Node.js: 22.20.0
V8: 13.8.258.32-electron.0
OS: Linux x64 6.18.2

For AI issues: which model did you use?

N/A

Does this stop you from using Cursor

Yes - Cursor is unusable

3

Hey, thanks for the report. This looks like an issue with the OAuth flow for Streamable HTTP servers on localhost. The logs show Cursor is trying to use OAuth (“Using OAuth scopes: mcp:connect”), but it fails on the POST request.

This is a known issue with HTTP-based MCP servers. Cursor doesn’t always open the browser correctly for OAuth auth. A similar case is described here: OAuth Browser Redirect Not Triggered for HTTP-based MCP Servers

To debug, I’ll need a bit more info:

  1. Can you share the full MCP logs? View > Output > select “MCP user-{your-server-name}” from the dropdown
  2. Do you see any errors in Developer Tools? Help > Toggle Developer Tools > Console tab
  3. What’s your config in mcp.json? (feel free to mask sensitive data)
  4. Does your localhost server require OAuth, or does it use simple header-based auth?

For now, try this workaround. If your server supports SSE transport instead of Streamable HTTP, or if you can pass auth via headers in mcp.json, it may help bypass the OAuth flow:

{
    "mcpServers": {
        "your-server": {
            "url": "http://localhost:3000/mcp",
            "headers": {
                "Authorization": "Bearer your-token"
            }
        }
    }
}
4 
1. local server provides OAUTH2 with DCR and authorization server discovery as defined in the RFCs. Works with MCP inspector and DIVE. DIVE instantly directs to the login page of the site after authorization connect to MCP server correctly.
2. Below is setting, but MCP server will return unauthorized for this token
3. Server uses self signed certificates. 
4. The output is shown as in the original post above. 
5. The error in output is 2026-01-12 22:34:14.109 [error] Client error for command Streamable HTTP error: Error POSTing to endpoint:  (as shown above)
6. using https (Secure) Cusrsor does not even make a call to the OAUTH or MCP endpoint logs attached. 
7. using insecure (http) cursor the logs for oath2 , mcp and cursor as attached
8. Server is PHP 8.x, Apache based, Ubuntu 25.10
9, OAuth2 and MCP server work fine with Dive and MCP inspector.
9. Settings:
{
  "mcpServers": {
    "localhost": {
      "name": "localhost",
      "type": "streamable-http",
      "streamable": true,

cursor.zip (3.2 KB)

     "url": "http://localhost/api/mcp/mcp",
      "headers": {
        "Authorization": "Bearer 12345"     }
    }
  }
}
5

Any additional information needed or any update ?

6

So this post is going to be another victim of ignore & expire auto-closure ?

7

Bump