How it finds your position
The checker requests the top 100 organic results in one call (num=100) and looks for the first result on your domain or a subdomain. If several of your URLs rank, all of them are highlighted.
Positions are organic positions: ads and other SERP features are not counted.
What it costs
Without a key, a check uses the keyless demo and counts against its small daily limit. With your API key, each check is one num=100 request, billed as a 7-credit depth bundle instead of 10 separate pages. Empty or failed results are refunded.
At the Pro pack price that's under half a cent per keyword. Put a nightly keyword list on the batch lane and it's 3.5 credits each.
Building a rank tracker
The Rank Tracker API page shows the full pattern: call POST /v1/rank with a keyword and a domain to get back just the position and matching URLs, or send up to 100 queries per call to POST /v1/batches, receive results on a signed webhook, and store only positions. See pricing for volume rates.
Do it with the API
Cost: 7 credits for the top 100. Failed and empty results are free.