Inspector not loading local variables

[tech4life87]

I been using inspector since yesterday with no issue. Had an update and now getting this error while not loading variables
@modelcontextprotocol/inspector@0.2.3
node version: 20.12.1

index-k3fLs7fd.js:185 
GET http://localhost:3000/config net::ERR_CONNECTION_REFUSED
(anonymous) @ index-k3fLs7fd.js:185
Ra @ index-k3fLs7fd.js:40
no @ index-k3fLs7fd.js:40
zf @ index-k3fLs7fd.js:40
tr @ index-k3fLs7fd.js:38
Dx @ index-k3fLs7fd.js:40
cr @ index-k3fLs7fd.js:40
_h @ index-k3fLs7fd.js:40
k @ index-k3fLs7fd.js:25
M @ index-k3fLs7fd.js:25
index-k3fLs7fd.js:185 Error fetching default environment: TypeError: Failed to fetch
    at index-k3fLs7fd.js:185:32453
    at Ra (index-k3fLs7fd.js:40:24263)
    at no (index-k3fLs7fd.js:40:42318)
    at zf (index-k3fLs7fd.js:40:36565)
    at tr (index-k3fLs7fd.js:38:3274)
    at Dx (index-k3fLs7fd.js:40:41221)
    at cr (index-k3fLs7fd.js:40:40215)
    at _h (index-k3fLs7fd.js:40:35675)
    at k (index-k3fLs7fd.js:25:1554)
    at MessagePort.M (index-k3fLs7fd.js:25:1919)

[ashwin-ant]

Can you share the command that you're using to start the inspector?

[tech4life87]

Can you share the command that you're using to start the inspector?
The default command generated from create-mcp-server command.
npx @modelcontextprotocol/inspector uv --directory /Users/user/s3-mcp-server run s3-mcp-server
as a workaround I am just reverting to previous version with
npx @modelcontextprotocol/inspector@0.2.2 uv --directory /Users/user/s3-mcp-server run s3-mcp-server

[ashwin-ant]

Are you able to run any of the example servers? Launching with this command works fine for me, for example:

npx @modelcontextprotocol/inspector uvx mcp-server-git

[jacksteamdev]

@ashwin-ant I'm experiencing this issue in some contexts. It depends on where and how I run the command. Unfortunately, I haven't been able to create a minimal reproduction.

The app created by npx @modelcontextprotocol/create-server works out of the box, but the inspector has quit working for a local project I've been working on.

In this screenshot, the inspector is trying to fetch from localhost:3000, but lsof -i :3000 shows no process is running on port 3000:

[jspahrsummers]

Could you try running the inspector by cloning this repository and then using npm run dev? That should give a better trace for any errors that occur.

[jacksteamdev]

This is a spawn error in my case. I still can't reproduce it reliably, but using npm run dev showed that at one point, spawn was throwing an ENOENT for the executable (in my case, bun, which looked like it should have been in the logged PATH).

Changing the command to the result of which bun got things working for me.

It would be nice to expose spawn errors in the inspector.

[ashwin-ant]

@jacksteamdev @tech4life87 we just released 0.2.7, which should address the issue. In particular it addresses a regression where the server would crash if there was an argument passed on the command line in the --arg format. If that's the issue you were seeing, can you try running against latest?