What Breaks Tracking After a Website Migration (and How to Prevent It)

Ask any media buyer what killed their tracking and you'll hear the same answer: “the client redesigned their site.” Migrations are the single most common cause of broken pixels and dead conversion tags — because the site looks perfect afterward while the tracking silently disappears.

Why migrations are so destructive

Tracking code lives in places developers don't always think about: theme files, header includes, tag manager containers, thank-you page templates. A migration rebuilds all of that. Unless someone explicitly owns tracking during the move, it gets left behind — and nothing visibly breaks, so nobody notices.

What actually breaks

• The pixel base code disappears. New theme, new header, no pixel. The most common failure by far.
• The Google tag / GTM container is missing. Same cause, different platform.
• Conversion trigger URLs change. If your conversion fires on/thank-you and the new site uses /order-confirmed, the trigger never matches.
• Server-side / CAPI integrations break. A replatform (Shopify → headless, WordPress → custom) usually severs the server-side integration entirely.
• Customer parameters get dropped. Even when events still fire, the hashed email/phone data may not — quietly tanking your Event Match Quality.
• Deduplication stops working. If the shared event_id logic isn't rebuilt, you get duplicate events.

Before the migration

1. Document every tracking asset: pixel IDs, conversion actions, GTM containers, CAPI integrations.
2. Screenshot current baselines — conversion volume, EMQ, duplicate rate — so you can compare after.
3. Put tracking in the launch checklist explicitly, with a named owner. “Someone will handle it” means nobody will.
4. Get the list of URL changes, especially conversion/thank-you pages.

Within an hour of launch

1. Run the Meta Pixel Helper and Google Tag Assistant on the new site.
2. Complete a real test conversion end to end and confirm it records in both platforms.
3. Check Events Manager for events received and any new diagnostics warnings.
4. Confirm conversion action status in Google Ads is still active.
5. Compare against your pre-migration baselines the next day.

The part people skip

Even a disciplined team checks on launch day and then moves on. But tracking often breaks on the seconddeploy — the bug-fix release a week later that quietly removes a tag. That's the failure nobody catches.

Taglert keeps checking long after launch day. It monitors pixel activity, EMQ, duplicate rate, and Google conversion tracking every 30 minutes across every account, so if a post-migration deploy breaks something in week three, you know in minutes instead of discovering it in a monthly report.