Gemini CLI session format

Store and files

Gemini CLI stores chats under ~/.gemini/tmp/<project-id>/chats/. If GEMINI_CLI_HOME is set, Gemini appends .gemini to that directory. deja can override only session reads with DEJA_GEMINI_ROOT.

Two generations coexist: whole-session .json files and replayable .jsonl files. projects.json maps working directories to project IDs; a per-project .project_root file is another observed source for the project name.

Records

Whole-session JSON has sessionId, startTime, lastUpdated, and a messages array. JSONL puts the session fields on its first metadata line, followed by message and control lines.

{"sessionId":"session-7","startTime":"2026-07-17T09:00:00Z","lastUpdated":"2026-07-17T09:00:02Z"}
{"id":"message-1","timestamp":"2026-07-17T09:00:01Z","type":"gemini","content":[{"text":"The configuration is valid."}]}

type: "user" maps to user; gemini and model map to assistant. Other types, including informational and error events, are ignored. Content is a string or an array of parts with text. All documented timestamps are RFC 3339; a missing message timestamp falls back to session start.

Resume

gemini --resume <uuid> takes the session id deja indexes — the --help text

mentions only latest and an index, but the CLI's own error names

--resume {uuid} and 0.55.1 accepts one. No cd: gemini scopes the lookup by

a hash of the working directory and stores only the hash, so there is nothing

to invert into a path. From the wrong directory it says "No previous sessions

found for this project" rather than opening someone else's.

Known quirks and drift

  • A resumed legacy .json session can be rewritten as .jsonl. deja deduplicates by session ID and prefers JSONL.
  • JSONL $set.lastUpdated patches session metadata.
  • $rewindTo replays history by removing the referenced message and everything after it before later records are applied.
  • The chats tree also contains non-session JSON such as checkpoints; files without a valid session ID and messages are ignored.
  • Nested subagent chat files occur below a parent chat directory.

Last verified: 2026-07-24

deja reads this format and nineteen others, and turns what it finds into memory your agents can search. See the harness matrix for what is wired where, or install it and search your own history.