xy — HTTP MCP server supervisor

Daemon + CLI that launches and supervises HTTP-based MCP servers.

Build

cargo build --release

Run

target/release/xy daemon       # foreground

Drop a server definition into $XDG_CONFIG_HOME/xy/servers/<name>.kdl (see examples/insikt.kdl) and xy reload.

Commands:

xy list
xy status <name>
xy start  <name|--all>
xy stop   <name|--all>
xy restart <name|--all>
xy reload
xy logs <name> [--tail N] [--follow]

Exit codes: 0 success, 1 operational error, 2 daemon unreachable, 3 config invalid.

Waiting on a dependency

A server can declare a precondition that must hold before it is started:

wait-for {
    path "~/.orbstack/run/docker.sock"
    timeout "180s"
    interval "1s"
}

Exactly one condition per block — path "<p>" (the path exists), tcp "<host:port>" (a connection succeeds), or command "<c>" with optional args (the process exits 0). timeout defaults to 120s and interval to 1s.

While waiting the server reports state waiting, and xy status <name> shows which condition it is blocked on and for how long. If the timeout expires the server is marked failed and is never spawned.

Waiting does not consume the restart budget: a slow dependency costs patience, not retries. This is what stops a Docker-backed server from being marked failed at login while the Docker daemon is still starting.

Servers that read stdin

MCP servers are stdio-first by convention, and several that also speak HTTP still start their stdio transport unconditionally. Under the launchd agent the daemon's stdin is /dev/null, so such a server sees EOF on its first read and shuts down seconds after binding its port.

stdin picks what the child gets on fd 0:

stdin "keep-open"

• inherit (default) — the child inherits the daemon's stdin.
• null — /dev/null; a read sees EOF immediately.
• keep-open — a pipe that xy holds open for the child's lifetime and never writes to, so a read blocks instead of seeing EOF.

Use keep-open for a server you want supervised in HTTP mode that insists on running its stdio transport anyway.

Start on login (macOS)

xy service install     # write the LaunchAgent, load it, start the daemon
xy service uninstall   # unload and remove the agent
xy service start       # load an installed agent
xy service stop        # unload until the next login
xy service status      # show agent state

xy service install snapshots the current PATH into the agent, because a launchd agent otherwise inherits only /usr/bin:/bin:/usr/sbin:/sbin and supervised servers would not find their toolchains. Re-run with --force after installing a new toolchain to refresh the snapshot.

xy service stop lasts until the next login. To disable start-on-login permanently, use xy service uninstall.

The daemon writes to $XDG_STATE_HOME/xy/logs/daemon.log. Failures that happen before the daemon starts logging — a missing binary, a malformed plist — are visible only to launchd:

launchctl print gui/$UID/se.aceofba.xy