Mac: Day One launches with a Dock icon but no window while the MCP server is run
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Day One for Mac 2026.22 (1791), macOS 27.0.1 (26A434), MacBook Pro (Mac17,9).
Since I enabled the Day One MCP server for Claude Desktop (Preferences > Labs > MCP Access Control), launching Day One sometimes shows the Dock icon but no window and no menu bar. It has survived every app update since roughly May. I traced the cause and can reproduce it on demand, so I am posting the details here in case it helps others and the team.
WHAT IS HAPPENING
The CLI installed by Day One > Install Command Line Tools is a symlink: /usr/local/bin/dayone points to /Applications/Day One.app/Contents/MacOS/dayone. When an AI assistant starts the MCP server it runs “dayone mcp”, a long-lived process that lives inside the app bundle. macOS LaunchServices registers that process as an application whose bundle path is /Applications/Day One.app, and it registers as a Foreground app because the CLI has no LSBackgroundOnly or LSUIElement setting. In lsappinfo list it shows as bundleID com.bloombuilt.dayone.cli, bundle path /Applications/Day One.app, type Foreground.
When I then click Day One in the Dock, macOS sees an app already running from that bundle and brings the MCP process to the front instead of starting the real app. That process has no windows, so nothing appears.
REPRODUCTION
With Claude Desktop running (so “dayone mcp” is alive) and the Day One app not running: pgrep -fl “Day One.app/Contents/MacOS/Day One$” prints nothing. Run open -b com.bloombuilt.dayone-mac. pgrep still prints nothing, and lsappinfo front shows the dayone mcp process is now frontmost.
Forcing a new instance starts the real app immediately, with its window, while the MCP server keeps running: open -n -b com.bloombuilt.dayone-mac. pgrep now shows /Applications/Day One.app/Contents/MacOS/Day One running.
So it is not a database lock and not a sync problem. The real app simply never gets launched.
WHAT I TRIED
Updating the app several times (no change). Killing every “dayone” process and relaunching (works, but it also kills the assistant’s Day One connection until the assistant restarts). Launching with “open -n” as above (works, nothing killed).
WORKAROUND FOR ANYONE HITTING THIS
In Terminal: open -n -b com.bloombuilt.dayone-mac
Or quit the AI assistant that is running the MCP server, then launch Day One.
SUGGESTED FIX FOR THE TEAM
Mark the dayone CLI as a background process (LSBackgroundOnly or LSUIElement in its embedded Info.plist), or have “dayone mcp” not register with LaunchServices, or install the CLI outside the app bundle. Any one of those should stop LaunchServices from treating the MCP server as the running copy of Day One.
I also posted this analysis on the open GitHub issue for the MCP server: https://github.com/bloom/dayone-mcp-server/issues/2
