Build a Custom Claude Code Statusline (with Rate Limits and a Bell on Done)

The default Claude Code statusline is honest but thin: model name, working directory, that's about it. After a few long sessions I wanted more from it. How much of the context window have I burned? Am I close to the 5-hour rate limit? Has the agent finished and I missed it because I was in another tab? Claude Code lets you replace the statusline with any shell command. It pipes a JSON blob to stdin on every render and prints whatever your script writes to stdout. So the upgrade is just bash and