A wellness add-on is an optional extra that may help with routine care costs, such as vaccinations or flea treatment, alongside insurance.
Standard pet insurance doesn't cover routine or preventative care. Vaccinations, flea treatments, worming, dental check-ups — these are excluded from the vast majority of policies because they're predictable, regular costs rather than unexpected ones.
A wellness add-on changes that, to a degree. Some insurers offer it as an optional extra on top of a standard policy, and it typically reimburses you for some or all of those routine costs up to a set annual limit.
Whether its worth having depends on what it actually covers and what it costs. Because the routine care it covers is predictable in cost, the premium for a wellness add-on tends to be priced at roughly what you'd spend anyway. Its not like illness cover where you might pay in for years and never need it — with a wellness add-on you're likely to use it regularly, which means insurers price it accordingly.
The other thing to check if you have a wellness add-on is whether you also have a vet health plan through your practice. If both cover vaccinations and flea treatment for example, you could end up paying for the same thing twice. Its worth going through both documents and checking for overlap.
Some wellness add-ons also include things like microchipping, dental cleaning or a contribution towards puppy training classes, so the value really does depend on what's in the specific version being offered.