Dynamic number insertion, explained
Dynamic number insertion (DNI) shows each website visitor their own phone number. When that number rings, you know exactly which visit, ad and keyword led to the call.
The problem DNI solves
A single tracking number on a website tells you that someone called from the website, and nothing else. But a website gets visitors from Google Ads, organic search, Facebook, email and a dozen directories. Without knowing which, you can't tell what to spend more on.
Giving each source its own fixed number works for print and directories, but not for a website, where every visitor sees the same page. DNI fixes that by changing the number for each visitor.
How dynamic number insertion works in Calltrail
- The Calltrail snippet loads on the page and reads where the visitor came from: the referrer, UTM tags and ad click IDs.
- It asks for a number from the client's pool and swaps it into the page, in the text and in tap-to-call links.
- That number is held for that visitor while they browse, and for a while after they leave.
- When it rings, the call is joined to the visit: source, campaign, keyword and landing page.
- Once the hold ends, the number goes back into the pool for the next visitor.
Session-level, not just source-level
Some tools only swap the number per channel, so everyone from Google Ads sees the same number. That tells you the channel, not the campaign or keyword. Calltrail gives each visitor their own number, so a call can be traced to the exact click.
It also matches forms: if someone fills in an enquiry form and later calls, both land on the same lead with the same source.
Fixed numbers for everything off the website
Google Business Profile, Checkatrade, Yell, Facebook ads that call directly, leaflets, radio and the side of the van each get a fixed tracking number of their own. Those calls are tracked in the same place as the website calls, so you see every source side by side.
Questions people ask
Does dynamic number insertion hurt SEO?
No. Search engines see your normal number in the page, and Calltrail only swaps it in the visitor's browser after the page loads. Your Google Business Profile and directory listings keep the number you give them, so your business details stay consistent.
How many tracking numbers do I need?
Enough that every visitor who might call in the next half hour or so can hold their own number. For most local businesses that's a handful. Calltrail shows how often the pool ran out and how many visitors held a number at the busiest moment, so you can add numbers only when needed.
What happens if every number is in use?
The visitor sees the business's main tracking number instead, so they can still call. That call is counted against the website as a whole rather than one visit.
Does it work with my website builder?
Yes. It's one script tag, so it works with WordPress, Wix, Squarespace, Shopify, Webflow and hand-built sites, or through Google Tag Manager.
Can people click to call on mobile?
Yes. Calltrail updates the number in tel: links as well as the text, so tapping the number dials the tracking number.
See your calls the way your clients wish they could
Book a 20-minute walkthrough. We'll show you Calltrail with sample clients, and set up your first tracking numbers if it suits.