How do I read the /context breakdown?

/context shows how full the model's context window is:

• Window size and % used, measured on the last step (or estimated before the first step).
• Breakdown: system prompt and session context, tool definitions (with the number of tools), your messages, replies, tool calls, tool results, free space.
• When auto-compact starts (about 80% of the window), with room kept for the reply.
• Number of messages in the history.

If tool results take most of the space, /compact helps. If tool definitions are large, consider disabling plugins or MCP servers you don't need.