Light Limits checks two limits, not one.

Two limits, and most guidance conflates them

There are two separate questions when you plug in a holiday display, and almost every guide online runs them together as though they were one sum.

The first is the circuit limit: how much total load the branch circuit can carry before the breaker trips. The second is the chain limit: how many sets you can connect end to end before the wiring inside the first set is carrying more current than it was built for. They have different causes and they give different numbers, and only one of them has a breaker watching it. Nothing protects you from exceeding the chain limit except knowing what it is.

It asks where you are first

Most holiday lighting guidance assumes a 120 volt American circuit, which leaves everyone on a 230 volt supply reading numbers that do not apply to them. Ring finals and 13 A fused plugs in the UK and Ireland change the answer; so does Australian and New Zealand practice.

So the site asks the region up front and then reports both limits independently, and tells you which one binds first. There are separate guides for the US and Canada, the UK and Ireland, and Australia and New Zealand, because the underlying rules are genuinely different rather than a units conversion.

Every constant is published

There's a methodology page listing every wattage, chain limit and circuit rule the calculator uses, and the standard each one comes from. It also names the places where we deliberately publish no number at all, because the honest answer is that it depends on something we can't see from here.

A safety calculator that won't show its working is asking for a kind of trust it hasn't earned. This one gives you something specific to argue with.