Do I need to declare an inheritance in Switzerland?
Yes, in most cases you should declare an inheritance, but whether you pay inheritance tax depends on the circumstances. Switzerland does not levy a federal inheritance tax, but many cantons have their own inheritance and gift tax rules. Inheritance tax, where applicable, is generally based on the deceased person's canton of residence and your relationship to them. Once you inherit assets, they also become part of your taxable wealth and must generally be declared in your Swiss tax return.

Dear taxum, I am expecting an inheritance. Do I need to declare it in Switzerland?
Possibly. But the picture is more nuanced than most people expect.
Switzerland has no federal inheritance or gift tax. What exists is a patchwork of cantonal rules - and they vary considerably depending on the canton and your relationship to the person leaving you the assets. Importantly, where inheritance or gift tax applies, it is generally levied by the canton in which the deceased person or donor was resident - not by the canton where the beneficiary lives.
In most cantons, spouses and direct descendants pay little or nothing. The further the family connection, the higher the potential tax. Some cantons tax gifts and inheritances from more distant relatives or unrelated parties at meaningful rates.
Assets inherited from abroad also need attention. They generally do not trigger Swiss inheritance tax - but they do need to be declared as part of your worldwide wealth from the year you receive them. The wealth tax clock starts immediately.
I have sat with clients who received an inheritance, assumed Switzerland had nothing to do with it, and were later surprised to find it sitting on their wealth tax assessment.
The inheritance itself may not be taxed. What you do with it afterwards very often is.