Find IE/Safari/old-Chrome-only crashes

Why this matters

Browser-specific bugs are the second-loudest support category after payment failures, and the hardest to reproduce on the dev laptop running the latest Chrome. The user emails “I clicked checkout and nothing happened” — you can’t repro, you close the ticket, they churn.

The actual cause is almost always: Safari 14.0 doesn’t support Array.prototype.at(), or some random old Chromium WebView used by an in-app browser is missing Promise.allSettled. Sentry shows you browser as a tag; segmenting by it is a manual filter you forget to apply.

Agentry’s HogQL can group errors by properties.$browser_version in one query. The bugs concentrated in one engine pop out instantly.

What you get

• A per-fingerprint browser distribution (what % of events came from which browser/version)
• Top 5 errors that are >80% concentrated in one browser version (= polyfill / compat issue)
• A “minimum browser version to support” suggestion based on your actual user mix

Walk through it

agentry_analytics_query {
  project_id: "default",
  hogql: "SELECT properties.fingerprint AS fp, properties.$browser AS browser, properties.$browser_version AS ver, count() AS cnt FROM events WHERE event = '$exception' AND properties.$lib = 'web' AND timestamp >= now() - INTERVAL 14 DAY GROUP BY fp, browser, ver HAVING cnt > 10 ORDER BY fp, cnt DESC"
}

{
  "rows": [
    { "fp": "f_c4a1", "browser": "Safari", "ver": "14.0", "cnt": 88 },
    { "fp": "f_c4a1", "browser": "Safari", "ver": "14.1", "cnt": 12 },
    { "fp": "f_c4a1", "browser": "Chrome", "ver": "120",  "cnt": 2 },
    { "fp": "f_98d2", "browser": "Chrome WebView", "ver": "90", "cnt": 64 },
    { "fp": "f_98d2", "browser": "Chrome", "ver": "121", "cnt": 1 },
    { "fp": "f_4e21", "browser": "Chrome", "ver": "121", "cnt": 410 },
    { "fp": "f_4e21", "browser": "Safari", "ver": "17.4", "cnt": 188 },
    { "fp": "f_4e21", "browser": "Firefox", "ver": "124", "cnt": 91 }
  ]
}

agentry_get_case { case_id: "f_c4a1" }

{
  "id": "f_c4a1",
  "error_type": "TypeError",
  "message": "undefined is not a function (evaluating 'arr.at(-1)')",
  "stack_top": "dist/app.js:bundled — fn name unknown"
}

The output

Browser-concentrated errors (14d, client-side only)

f_c4a1   TypeError: undefined is not a function (evaluating 'arr.at(-1)')
         97% Safari 14.x   (100 events / 102 total)
         3% other          (2 events)
         ↗ Polyfill `Array.prototype.at` OR replace with `arr[arr.length - 1]`

f_98d2   ReferenceError: globalThis is not defined
         98% Chrome WebView 90  (64 events / 65 total)
         2% other               (1 event)
         ↗ Old in-app browser. Check who's embedding you (referrer logs)

User-mix context (last 14d, all events):
   Chrome 120+      62%
   Safari 16+       21%
   Safari 14-15      4%   ← f_c4a1 users
   Firefox 120+      9%
   Chrome WebView    1%   ← f_98d2 users
   Other             3%

If we drop Safari < 16, we lose ~4% of traffic but kill f_c4a1
and 3 other latent compat bugs.

Setting it up

If you’re already capturing client-side errors via raw fetch, the User-Agent of the browser is auto-attached by the server. To make the slice richer (especially for HogQL), also send $browser / $browser_version in properties — the PostHog-shaped alias /v1/track/ does this automatically when called from posthog-js, but if you’re rolling your own you can parse and send:

// In your browser-side error handler
window.addEventListener("error", async (ev) => {
  await fetch(`https://api.agentry.sh/v1/logs/${PROJECT_ID}/`, {
    method: "POST",
    headers: {
      "Authorization": `Bearer ${AGENTRY_DSN}`,
      "Content-Type": "application/json",
      "User-Agent": "myapp-web/1.0",  // REQUIRED — Cloudflare 403s default UAs
    },
    body: JSON.stringify({
      message: ev.message,
      stack: ev.error?.stack,
      url: window.location.href,
      user_agent: navigator.userAgent,
      tags: {
        $lib: "web",
        // Optionally pre-parse for cleaner HogQL queries:
        // $browser: parsedUa.browser,
        // $browser_version: parsedUa.major,
      },
    }),
  });
});

The server parses user_agent into $browser / $browser_version for you, so you don’t strictly need to pre-parse — but doing so means HogQL queries work without JSONExtract gymnastics.

Variations

• “Same query but only for users on our paid plans — do enterprise customers have a different browser mix?”
• “Which OS versions are concentrating errors? iPhone 14.x = old iOS, Android 9 = old Chrome WebView.”
• “Find errors that only happen on mobile (any browser, screen width < 768).”
• “Are there errors only on Cypress/Playwright user agents? Probably a flaky test, not a real bug.”