Feedback: Throws error on Unsupported protocol version #959
Description
Inspector Version
0.17.5 latest
Describe the bug
The inspector seems to fail with some older servers I have:
McpError: MCP error -32602: Unsupported protocol version: 2025-11-25 - supported versions: 2025-06-18,2025-03-26,2024-11-05,2024-10-07
McpError http://localhost:6274/assets/index-CneFQkmB.js:16182
fromError http://localhost:6274/assets/index-CneFQkmB.js:16197
_onresponse http://localhost:6274/assets/index-CneFQkmB.js:27833
onmessage http://localhost:6274/assets/index-CneFQkmB.js:27626
processStream http://localhost:6274/assets/index-CneFQkmB.js:42007
_handleSseStream http://localhost:6274/assets/index-CneFQkmB.js:42039
send http://localhost:6274/assets/index-CneFQkmB.js:42166
request http://localhost:6274/assets/index-CneFQkmB.js:28055
request http://localhost:6274/assets/index-CneFQkmB.js:27941
connect http://localhost:6274/assets/index-CneFQkmB.js:40972
connect http://localhost:6274/assets/index-CneFQkmB.js:42829
Nb http://localhost:6274/assets/index-CneFQkmB.js:1277
Tb http://localhost:6274/assets/index-CneFQkmB.js:1289
Ub http://localhost:6274/assets/index-CneFQkmB.js:1292
nf http://localhost:6274/assets/index-CneFQkmB.js:2229
se http://localhost:6274/assets/index-CneFQkmB.js:2252
hd http://localhost:6274/assets/index-CneFQkmB.js:2524
Qk http://localhost:6274/assets/index-CneFQkmB.js:5828
Jb http://localhost:6274/assets/index-CneFQkmB.js:1230
hd http://localhost:6274/assets/index-CneFQkmB.js:2325
fd http://localhost:6274/assets/index-CneFQkmB.js:1723
ed http://localhost:6274/assets/index-CneFQkmB.js:1706
It seems that the inspector is sending the 11-25 protocol and my servers aren't negotiating correctly (something I think I'll need to go and fix). This wasn't immediately intuitive to me since the inspector just showed "Connection Error - Did you add the proxy session token in Configuration?" error.
To Reproduce
Steps to reproduce the behavior:
- Use a server that doesn't support the newer spec
- This server sends a
-32602MCP error indicating it doesn't support a protocol version - Notice no helpful error in MCP inspector
Expected behavior
It'd be very helpful, as a server builder to see these errors surfaced more easily.
Inspector V2 is under development to address architectural and UX improvements. See CONTRIBUTING.md for information about V2 development.