Travel to the United Kingdom is starting to get more complicated. Starting January 8, 2025, you will need to apply for an Electronic Travel Authorization (ETA) to visit the United Kingdom. This new ETA is a digital registration scheme for travelers who do not need a visa to enter the UK. What it is a mandatory, paid for authorization to travel with security clearance done in advance.
The 48 countries that are eligible for the ETA can be found here. If you are too lazy to click the link, the 48 countries are:
Antigua and Barbuda, Argentina, Australia, The Bahamas, Barbados, Belize, Botswana, Brazil, Brunei, Canada, Chile, Costa Rica, Grenada, Guatemala, Guyana, Hong Kong Special Administrative Region (including British national overseas), Israel, Japan, Kiribati, Macao Special Administrative Region, Malaysia, Maldives, Marshall Islands, Mauritius, Mexico, Federated States of Micronesia, Nauru, New Zealand, Nicaragua, Palau, Panama, Papua New Guinea, Paraguay, Peru, Samoa, Seychelles, Singapore, Solomon Islands, South Korea, St Kitts and Nevis, St Lucia, St Vincent and the Grenadines, Taiwan (if you have a passport issued by Taiwan that includes in it the number of the identification card issued by the competent authority in Taiwan), Tonga, Trinidad and Tobago, Tuvalu, United States and Uruguay.
It will cost you £10 (about $12.50), and you can apply through the official app listed on the UK government website, or directly online.
The application will take about 20 minutes and you will need to answer questions and upload a photo of yourself. Expect an answer within 3 days. The best part is that an ETA is valid for 2 years. You can use the ETA as frequently as you want but stays must be shorter than 6 months.