Session Replay (Time Machine)

Time Machine replays a participant's session frame by frame, so you can see exactly what they experienced, understand why each thing happened, and even explore "what-if" alternatives.

Open a replay

From Monitor, find the session and click Replay (or open the session detail and choose View Replay). This opens the replay view at /app/studies/<studyId>/replay/<sessionId>.

Step through it

Replay is keyboard-driven:

Key	Action
`Space`	Play / pause
`←` / `→`	Previous / next frame
`Shift`+`←` / `Shift`+`→`	Previous / next trial
`Home` / `End`	First / last frame
`E`	Toggle Explain
`B`	Toggle Branches
`S`	Copy a share link to the current frame
`1`–`8`	Playback speed presets

Explain: the "why" behind a frame

Press E to see the provenance of the selected frame — the condition assignment, timing, trial order, resolved bindings, and policy decisions that produced it.

No lies

Explain follows a strict honesty rule: if a value can't be proven from captured data, it shows "unknown / not captured" rather than guessing. A session missing some metadata will replay with Explain listing the fidelity gaps.

Branches: what-if exploration

Press B to branch from the current frame: apply patches (parameter changes, design-row edits), execute the branch, and compare outcomes against the original. You can export a branch as a portable JSON "config patch" that carries its provenance (session, run, bundle hash, fork point) — useful for sharing a precise reproduction or a proposed fix.

When it helps

Reach for Time Machine when a session's data looks wrong, a participant reports an issue, or you want to confirm a design change would have behaved differently — without re-running anyone.