What Is Session Replay? Uses, Risks, Privacy
Session replay defined: how visit reconstruction works, the privacy and consent stakes, and privacy-first ways to get the insight.
Session replay reconstructs a visitor's session as watchable video — every scroll, click, hesitation, and keystroke, rebuilt from recorded DOM mutations and input events. As a debugging and UX tool it is genuinely powerful; as a data practice it is the most invasive thing in mainstream analytics, and the gap between those two sentences is where teams get into trouble.
How it works
A recording script serializes the DOM and streams every mutation and interaction to the vendor. Playback re-renders it all in order — which means by default the recording includes whatever users typed, hovered, and revealed: form fields, account data on screen, the email half-typed into the wrong box. Masking features exist; masking configuration errors are an entire genre of data-breach disclosure.
The three costs
- Privacy and consent: recording behavior at keystroke granularity is personal-data processing well past 'audience measurement' — consent is required in EU contexts, and the recording vendor joins your DPA sub-processor list holding your most sensitive stream.
- Performance: observing everything costs tens-to-hundreds of KB plus continuous main-thread work — a direct INP tax on every recorded visitor.
- Attention: replays are seductive and slow; teams watch hours to learn what an aggregate would have said in seconds. The honest use case is narrow: forensic investigation of specific reported problems.
The privacy-first version of the insight
Most forensic questions — what did the user who hit the bug experience? where did the checkout die? — are answered by a per-visitor timeline: pages, clicks, load times, and JavaScript errors in sequence, no keystrokes recorded, no video stored, no consent wall triggered. It reads like a flight recorder rather than surveillance footage, which is both the ethical and the practical point (the full Hotjar-class comparison). Clycyo ships the timeline natively — judge whether it covers your replay needs on real data at /open.
If you do run true replay: consent-gate it, mask aggressively, sample sparsely, and retain briefly. Power tools deserve guards.