How to track a competitor's Amazon best-seller rank and price history
Today's best-seller rank is a snapshot. To understand a competitor, you need the trend: is the rank rising or falling, did they cut the price to get there, are reviews growing, and did they run out of stock?
What to look at
- Best-seller rank (BSR) over time. Lower is better, and it's the closest public proxy for sales. A falling number means rising sales.
- Price over time: the current price, the 90-day range and the average. Did a climb come from a price cut?
- Reviews gained: how fast the review count grows tracks sales volume.
- Days out of stock. Stockouts explain sudden rank drops, and repeated ones are an opening for you.
- Launch date and "bought in past month" give context for how new and how big the product is.
Reading the patterns
| Pattern | Likely meaning |
|---|---|
| Rank climbing, price flat | Organic momentum, ads, or a listing improvement. Check what changed. |
| Rank climbing, price falling | Buying growth with discounts. Watch whether the rank holds when the price returns. |
| Rank falling with out-of-stock days | Supply problem, not demand. Their buyers are looking elsewhere right now. |
| Rank falling, in stock, price flat | Losing to competitors: new entrants, worse reviews or reduced ads. |
| Review count dropping | Usually Amazon merging or splitting variation listings, not lost reviews. |
A real example
In October 2026, a thick yoga mat (B07H9PZDQW) went from best-seller rank #129 to #7 in Sports & Outdoors over 90 days. Its price stayed flat at about $25, it gained about 578 reviews, and it had no stockouts, with most of the move in the final two weeks. In the same category, a mat out of stock on 27% of days fell from #301 to #1,635.
Ask your AI: "Has [ASIN] been growing over the last 90 days? Show its rank, price and review trend." In Claude, the answer usually includes a weekly rank chart.
How often to check
Monthly for your top 5 competitors is plenty. Check more often around big sale events (Prime Day, Black Friday) to see who discounts and whether it worked.
Questions
Where does the history come from?
ZonRival's price and rank history comes from Keepa, which has tracked Amazon prices and ranks for over a decade, used with Keepa's permission. It covers 10 marketplaces: US, UK, Germany, France, Italy, Spain, Canada, India, Japan and Mexico.
How far back can I look?
From 7 days up to a year. 90 days is a good default for spotting momentum.
Is best-seller rank the same as sales?
No, but it's the best public proxy. Rank is relative to other products in the same category and updates frequently, so compare trends rather than single readings.
Try it on your own competitors
ZonRival plugs into Claude and ChatGPT as a connector. Sign in with Google and you get 25 free credits, enough for a few full teardowns. Read-only; 12 Amazon marketplaces.