Session replay

Replay records the DOM as a stream of mutations using rrweb (the same library Sentry uses). When an error fires, the SDK attaches the most recent buffer to the envelope. The dashboard re-runs the recording so you can scrub through the last 30 seconds before the crash.

Enable in the SDK

Add the replayIntegration when you initialize Sentry. Use replaysOnErrorSampleRate: 1.0 to capture every error, and replaysSessionSampleRate: 0 to keep continuous-session recording off (much cheaper, much less PII risk):

Sentry.init({
  dsn: "<YOUR_DSN>",
  replaysSessionSampleRate: 0,
  replaysOnErrorSampleRate: 1.0,
  integrations: [
    Sentry.replayIntegration({
      maskAllText: true,
      maskAllInputs: true,
      blockAllMedia: true,
    }),
  ],
});

Privacy defaults

GlitchReplay's recommended defaults are stricter than Sentry's:

• maskAllText: true — all text content recorded as ***
• maskAllInputs: true — input values never recorded
• blockAllMedia: true — <img>, <video>, <canvas> rendered as placeholders

These should be your starting point even on internal apps. To selectively unmask elements you trust:

<div data-sentry-unmask>This text appears in replay.</div>
<div class="sentry-unmask">Same effect.</div>

And to block elements that would otherwise be unmasked:

<input data-sentry-mask />     <!-- value masked -->
<div data-sentry-block />      <!-- entire subtree blocked -->

What it costs

• Free plan — replay disabled.
• Pro / Business / Enterprise — replay included; no per-replay charge.

Sentry charges $6 per 1,000 replays on top of their Business tier. We don't.

How replays are stored

rrweb events are stored in R2 next to the raw envelope, keyed by {project_id}/{event_id}/replay.json. The dashboard's replay player streams them back on demand — there's no server-side rendering, so scrubbing is instant once the file is fetched.

Replay summary (AI)

On Pro and above, each replay is summarized into a one-sentence narrative — "User opened the search modal, typed ‘invo’, hit Enter, then the page froze." — generated from the breadcrumb stream alone (no DOM content, no PII risk). Useful for triaging a list of issues without opening each one.

What replay does not do

• It's not a UX-research tool. Don't use it for funnel analysis.
• It doesn't cover server-side or RSC errors that never touched the browser. For those, replay is empty (the error event still ingests).
• It doesn't record cross-origin <iframe> contents.

Next: configure alerts for new issues with replay, or read about PII scrubbing.