93% of a Claude Code Session Is Noise. Here's the Proof.

I wrote a session distiller for Claude Code that cuts 70MB sessions down to 7MB. That post covered the what and how. This one covers the why, with data. Before I wrote a single line of code, I needed to answer three questions: What's actually inside a 70MB session? What's safe to throw away? How do I prove I'm not losing anything that matters? Dissecting a 70MB Session I opened a real 70MB session JSONL and categorized every byte. Here's the breakdown: JSON envelope (sessionId, cwd, version, gitBranch): ~54% Tool results (Read, Bash, Edit, Write, Agent): ~25% Base64 images (screenshots, UI captures): ~12% Thinking blocks (internal reasoning): ~4% Actual conversation text: ~3% Progress lines, file-history-snapshots: ~2% That first line is the surprise. Every single JSONL line repeats the same envelope fields: sessionId, userType, cwd, version, gitBranch, entrypoint. Same values, every line. On a 70MB file with thousands of lines, that's 38MB of identical JSON keys and values repeated ov