Every conversation you have with Claude Code is written to disk as JSONL, under ~/.claude/projects/. Your decisions, your dead ends, the bug hunt that took three sessions: it is all there. You have probably never opened one.
The catch: the format is an internal implementation detail. No documentation, no version field, no stability guarantee. The schema changes whenever the CLI updates, which is, at the current pace, almost daily.
The patterns below come from building a read-only replay and search tool on top of these files, and from keeping it alive through a dozen CLI releases. Each pattern survived contact with real data. Four were learned the hard way, from bugs worth retelling.
The ground rule: you are an archaeologist, not a validator
A parser for someone else's internal format has a different job than a parser for your own API. Rejecting malformed input is not an option: the input is the historical record, and whatever is on disk is all there will ever be.
