What Is Session Replay? How It Works and When to Use It
Session replay lets you watch what real users did on your site — and why they got stuck. Here is how session recording works, what it captures, and when it is (and is not) the right tool.
Dmytro Vavreniuk
Product Engineer
Session replay is a way to record a visitor's session on a website or web app and play it back later, so you can see the clicks, scrolls, form interactions, page changes and errors that led to a problem. Analytics tells you that 40% of users dropped off at checkout; session replay shows you what happened.
What session replay is (and what it is not)
A session replay tool, sometimes called a session recording tool, captures a user's visit as a stream of events and reconstructs it in a player. You get a timeline you can scrub through, usually with the page as the user saw it, a cursor, click markers, and a log of console messages and network requests alongside.
It is not screen-capture video. Recording real video of every visit would be heavy, expensive to store and impossible to privacy-filter. Instead, modern session recording works on structured data about the page, which is why a replay can be small, searchable and safe to mask.
How session replay works
Under the hood, most web session replay follows the same four-step pipeline. If you want the full engineering detail, we cover it in session replay architecture, from data flow to playback and in our free 200-page book on how session replay works.
- Snapshot. When the page loads, a small script serializes the current DOM (the page's structure, text and styles) into a compact snapshot.
- Observe. From then on, a
MutationObserverand event listeners record every change: nodes added or removed, attributes updated, mouse moves, clicks, scrolls, input events, viewport resizes. - Batch and send. Events are compressed, batched and sent asynchronously to a collector, so recording does not block the user's interaction.
- Replay. In your dashboard, a player rebuilds the snapshot inside a sandboxed iframe and re-applies the events in order, at the original timing.
Because the player rebuilds the page rather than playing a video, replay can be sped up, skip idle time, jump to the exact click that triggered an error, and be searched by URL, user attribute or error message.
What session recording captures
- Page views and navigation, including single-page-app route changes
- Mouse movement, clicks, rage clicks and dead clicks, scrolling
- Form interactions (with sensitive fields masked)
- JavaScript errors and console output
- Network requests, status codes and timings
- Device, browser, viewport and connection context
When to use session replay
Session replay is strongest when you already know something is wrong but not why. The most common uses:
- Reproducing bugs. Instead of asking a customer for steps to reproduce, watch the session where it happened. See how to debug frontend bugs with replay and error tracking with session replay.
- Diagnosing funnel drop-off. Your analytics shows a step losing users. Replays of sessions that abandoned that step show confusing copy, a broken button or a slow response.
- Finding UX friction. Rage clicks, repeated back-and-forth navigation and hesitation over a field are all visible in a replay long before they show up in a metric. For a worked example you can play in the page, see the hunt for justify-content, a session replay case study.
- Supporting customers. Support can open the session linked to a ticket and see exactly what the user saw.
- Validating releases. After a deploy, watch real sessions on the changed flow to confirm it behaves as intended.
Session replay vs analytics vs heatmaps
These tools answer different questions, and they work best together:
| Tool | Answers | Weakness |
|---|---|---|
| Product analytics | How many, how often, where users drop | Does not explain why |
| Heatmaps | Where users click and scroll in aggregate | No individual story or sequence |
| Session replay | What one user actually did, step by step | Time-consuming without filters |
For a deeper comparison, read heatmaps vs session replay: when each wins.
When session replay is the wrong tool
Replay is not a replacement for everything. It is a poor fit for answering aggregate questions (use analytics), for sites with very low traffic where you would be watching a handful of sessions anyway, or for any flow where you cannot mask the sensitive data on screen. Watching sessions at random is also a time sink: always start from a filter, such as sessions with an error, sessions that abandoned checkout, or sessions from a specific release.
Privacy: what to mask and how
Recording user sessions means handling personal data, so privacy is part of the setup, not an afterthought. Good practice is to mask all inputs by default, block elements that show personal data (account pages, payment forms, messages), sanitize the DOM in the browser before upload, set a sensible retention period, and disclose the recording in your privacy policy. In the EU you will usually also need a lawful basis such as consent. Our guide to privacy-first session recording in the EU walks through the details, and a dedicated post on GDPR, masking and consent is coming in December.
How to choose a session replay tool
Look at five things: how masking is enforced (client-side, by default), the performance cost of the recorder, whether replays are linked to errors and network data, how you filter and search sessions, and pricing at your traffic level. We compared pricing and features across a dozen vendors in session replay tools compared.
Getting started with LogNroll
LogNroll bundles session replay, heatmaps, error tracking and product analytics, with a free tier of 1,000 sessions per month. Setup is a single script or npm package; the quickstart guide takes a few minutes. If you are still weighing the case for it, read why session replay is essential for web teams.
Frequently asked questions
What is session replay?
Session replay (also called session recording) is a technique that records what a visitor does on a website or app — clicks, scrolls, typing, navigation, errors — and lets you play it back later as a video-like reconstruction of the visit.
Is session replay a real video?
No. Most tools record DOM changes and events as small structured data, then rebuild the page in a sandboxed player. This is far lighter than screen video and lets sensitive fields be masked before data leaves the browser.
Is session recording legal?
It can be, if you mask personal data, disclose the recording in your privacy policy, and obtain consent where required (for example under GDPR in the EU). Rules differ by region, so check with your legal team.
Does session replay slow down my site?
A well-built recorder adds a small script, batches events and sends them asynchronously, so the impact on page load is usually minimal. Measure it on your own pages before and after rollout.
See what your users actually do. Start session replay for free.