The 56% on conversation turns with no tool usage matches what I've seen too. A lot of that is Claude thinking out loud, context management, and planning before it touches anything. It feels wasteful until you realize the alternative is it immediately starts editing files without understanding the codebase first.

The JSONL transcript parsing is clever. I've been reading those same files for a different purpose (rendering conversation history in a menu bar app) and the format is more reliable than I expected. Each tool call has enough metadata to reconstruct what happened without needing to re-parse the full conversation.

One thing that would be interesting to see: cost broken down by session when you're running multiple sessions in parallel. Right now I have no idea which of my 4 running sessions is burning the most tokens.