Dynamic number insertion

Dynamic number insertion (DNI) is the website half of call tracking. A script finds the business's phone number on the page, in tel: links and in the text, and replaces it with a number from a pool. The service remembers which visit each number was lent to. When that number rings, the call takes on the visit's source, UTM parameters and ad click id.

A number stays with one visitor for a while after their last page view, often around 30 minutes. If more people are on the site at once than the pool holds, a number must be reused and a call on it could belong to either visitor, so the pool is sized to the busiest moment, not to monthly traffic.

Because the swap happens in the visitor's browser, the real number stays in the page's HTML, which keeps business listings consistent for search engines. See call tracking for local businesses.