Server-side Seznam Sklik conversions for the Czech market

Why SEM with DataNostro?

Seznam Event Measurement (SEM) is Seznam's new unified measurement standard — a single sul.js script replaces the old separate retargeting (rc.js) and conversion codes. The client-side sul.js alone loses 20–35% of events to ad-blockers and Safari ITP. The server-to-server layer recovers that loss — but sul.js still has to run.

SEM runs as client + server

S2S is not a standalone solution. The sul.js script must run in the browser — it sets the sid and udid cookies (only after ad_storage consent) and measures client-side. DataNostro then reads those cookies on the server, hashes personal data with SHA-256 and sends the event with a separate S2S SEM ID to sem.seznam.cz/rtgconv — asynchronously, never blocking order processing. Client + server together = more complete, more resilient measurement.

What SEM adds over the old codes

• One script instead of separate retargeting and conversion codes
• Multiple event types with detailed reporting
• Automatic retargeting from events (no manual lists)
• Consent via IAB TCF or Google Consent Mode
• Server-to-server as a complement to client measurement (requires sul.js)

Setup in DataNostro

Connect your Sklik account, deploy sul.js and enter the separate SEM ID for S2S. The same "purchase" event is sent to GA4, Meta CAPI, Google Ads and SEM at once — one source, attribution across every system. Works with Shopify and WooCommerce.