1. Install Node.js 22 or newer
From nodejs.org or Homebrew (brew install node). The agent has zero runtime dependencies of its own, so there is nothing else to install.
2. Download the release and run it once
Unpack the release tarball for the current agent version, then REALUPTIME_TOKEN=rua_... node dist/agent.js. Watch the log for the polled line, which means the token works.
3. Make it a launchd job
Write a LaunchDaemon plist under /Library/LaunchDaemons that runs node dist/agent.js with REALUPTIME_TOKEN in EnvironmentVariables and KeepAlive true, then launchctl load it. The agent reads vm_stat, df, netstat, ps and launchctl list with fixed arguments, and nothing else, to build its sample.
4. Watch services if you want to
On the agent's server health page, list the launchd labels you care about (com.apple.sshd, your own io.example.worker) under Watched services. Each reports active, inactive or failed on the next sample.
Go deeper
The full reference lives in the docs: Monitor agent documentation. Error codes named above are each explained in the error-code reference.