Is chiptuning legal?

Adjusting engine software for more power isn't prohibited. There's no law saying your car has to stay on factory settings.

The vehicle does have to keep meeting the requirements for road use. That means among other things that emissions stay within the limits of the type approval and that all emission control systems are present and working.

Removing or disabling emission control systems is not permitted for vehicles used on public roads. That covers the particulate filter, the EGR, the AdBlue system and the catalytic converter, among others.

For the particulate filter it has been a criminal economic offence in the Netherlands since October 2018. Since January 2023 the annual test physically checks whether the filter is present. The penalty is set by a judge and ranges from a fine to imprisonment.

An important detail people often get wrong: the offence is the removal or disabling itself, not driving with it. A declaration that the car only sees track use changes nothing. And the penalty can be imposed on the business carrying out the work, not just on the owner.

This is different. On passenger cars the limiter isn't a legal requirement but an agreement between manufacturers. Removing it is allowed and the car won't fail its annual test for it.

The speed rating of your tyres does become the new limit. A tyre rated V is approved to 240 km/h; going beyond that is dangerous and not covered. On trucks and buses over 3.5 tonnes the limiter is legally required.

A software adjustment that stays within the limits is no problem at the annual test. The contents of the engine software aren't inspected.

What is inspected: the presence of the particulate filter, emissions during the test, and whether there are active fault codes relating to emissions.

Even a fully legal modification has to be reported to your insurer. If you keep quiet and something happens, the insurer can limit or refuse cover. That isn't a matter of legislation but of your policy terms.