Top-of-search impression share (TOS IS)

Amazon's definition is narrow and worth reading literally: the percentage of top-of-search impressions your campaign received out of the total top-of-search impressions it was eligible to serve on. The block is small and device-dependent — Amazon's placement help defines top of search (first page) as up to the first 5 positions in the top row of page-one results on desktop and up to the first 4 on mobile. It exists for Sponsored Products and Sponsored Brands only, carries a 90-day lookback, and can lag up to 12 hours in campaign manager. On grain, Amazon's own Ads API v3 documentation disagrees with itself about whether the metric is available at target level, so pull it yourself before you build a bid rule on it.

Two traps. Grain: on an exact-match keyword the number means what you think; on broad, phrase, auto or product targets it is a weighted average over queries you cannot see — 40% might be 90% on a long-tail variant and 5% on the head term. The Search Term Impression Share report does not patch this hole: its denominator is every advertiser's impressions on the term, across all placements. Second, bidding: the placement adjustment adds to your bidding strategy rather than capping it. Amazon's example takes a dynamic $1.00 bid to $1.50 with a 50% adjustment, and dynamic bidding (up and down) can push it up to $3.00. Amazon publishes no benchmark, so treat TOS IS as directional: single-keyword campaigns for clean grain, one multiplier at a time, read after the 12-hour lag.