Why I Started Watching My Claude Code Context Window (And Built Something to Track It)

If you're using Claude Code heavily and not paying attention to your context window, you're probably paying more than you need to. Here's why it matters and what I changed. The thing most people don't realize Every time you send a message in Claude Code, the entire conversation history gets sent with it. Not just your new question. Everything. Every file you pasted, every response Claude gave, every back-and-forth since you opened the session. This means cost doesn't scale with message length. It scales with accumulated context. If your context window is at 70% and you ask something simple like "can you rename this variable?", you're paying for the full 70% of history sitting behind that tiny question. The question itself is almost irrelevant to the token count. Once this clicked for me, I couldn't unsee it. What actually drives your token costs Let's make this concrete. Say you've been in a Claude Code session for two hours. You've pasted several files, iterated on a feature, debugged