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Kubernetes MCP server tools fail with TypeError: output.output.toLowerCase #12987
Description
Description
All tools from kubernetes-mcp-server (v0.0.57 by containers/kubernetes-mcp-server) fail with:
TypeError: undefined is not an object (evaluating 'output.output.toLowerCase')
The MCP server itself works correctly — tested directly via JSON-RPC over stdio, it returns valid MCP responses. The issue is in OpenCode's MCP client response parsing.
Direct JSON-RPC test (works):
{"jsonrpc":"2.0","id":1,"result":{"content":[{"type":"text","text":"APIVERSION KIND NAME..."}]}}Same call through OpenCode → TypeError
Every tool fails identically: namespaces_list, pods_list, configuration_view, events_list, helm_list, etc.
Plugins
[email protected] (containers/kubernetes-mcp-server)
OpenCode version
1.1.53
Steps to reproduce
- Configure
.mcp.jsonwith kubernetes-mcp-server:
{
"mcpServers": {
"kubernetes": {
"command": "npx",
"args": ["-y", "kubernetes-mcp-server@latest"],
"env": {
"KUBECONFIG": "./kubeconfig/my-cluster.yaml"
}
}
}
}- Open OpenCode and invoke any kubernetes MCP tool (e.g.
namespaces_list,pods_list) - All calls fail with:
TypeError: undefined is not an object (evaluating 'output.output.toLowerCase')
Operating System
macOS 26.3 (Apple Silicon / arm64)
Terminal
Warp, Ghostty
Activity
scw1109 commentedon Feb 10, 2026
Seeing same for using playwright-mcp and mcp with google toolbox.
However, my error only being seen via OpenCode ACP, does not seeing it if using TUI.
Nenormalniy commentedon Feb 10, 2026
Same bug on Windows 11 with my custom mcp server.
Also, do you use OMO plugin?
Is the problem related with this release?: https://github.com/code-yeongyu/oh-my-opencode/releases/tag/v3.5.0
code-yeongyu/oh-my-openagent#1720
rollback to [email protected] fixed this issue for me
kamafozilov commentedon Feb 10, 2026
yeah, I use OMO too, but I haven’t had any issues with OMO on my side
blackbxdev commentedon Feb 10, 2026
Pinning OMO solved my issue as well. Thank you for this!
roshitx commentedon Feb 11, 2026
Confirmed - Affects ALL MCP Servers
I can confirm this bug affects all MCP integrations, not just Kubernetes MCP:
Root Cause: Client-side parser expects
response.output.outputbut MCP servers returnresponse.outputWorkaround for Laravel Boost users:
Additional Details: #13091
ouchxp commentedon Feb 11, 2026
Temporary fix -> add it to oh-my-opencode.jsonc
"disabled_hooks": ["comment-checker"], // Temporarily added to address bug in 3.5.1 (MCP)
code-yeongyu/oh-my-openagent#1737 (comment)
github-actions commentedon Apr 13, 2026
To stay organized issues are automatically closed after 90 days of no activity. If the issue is still relevant please open a new one.