Remote server lists the app-only ui_get tool to clients without MCP Apps support #3683

Hi! While testing the remote server, I noticed that ui_get is listed to every client, including ones that don't support MCP Apps.

The tool is marked for the app only:

{
  "name": "ui_get",
  "_meta": { "ui": { "visibility": ["app"] } },
  "description": "Fetch UI data for MCP Apps (labels, assignees, milestones, issue types, branches, issue fields, reviewers)."
}

An MCP Apps host reads that and keeps the tool away from the model, which is what you want. But a client without MCP Apps support doesn't look at _meta.ui at all, so it hands ui_get to the model as a regular tool. The model then sees a helper meant for a UI widget, and every conversation pays tokens for its schema.

The MCP Apps spec suggests checking client capabilities before registering UI tools. A client that supports Apps declares extensions["io.modelcontextprotocol/ui"] in its capabilities, so ui_get could be left out when that's missing.

To reproduce: list tools with a PAT twice, once with empty client capabilities and once with {"extensions": {"io.modelcontextprotocol/ui": {"mimeTypes": ["text/html;profile=mcp-app"]}}}. On both /mcp (49 tools) and /mcp/readonly (29 tools), ui_get shows up both times.

It's minor, since the tool is read-only. Tools like get_me that are visible to the model and the app are fine to list to everyone; this is only about the app-only one.

For context, I found it with toolmenu, a linter for MCP tool lists, on 2026-11-05. The server identified itself as github-mcp-server/remote-cffc9f76.