What website builder is 100% free?

If you mean “no monthly fee for the builder,” Google Sites is one of the closest to truly free for basic websites. The tradeoff is flexibility and branding control compared to paid builders. If you mean “free with a custom domain,” that is rarely truly free long-term because domains and business-grade features cost money somewhere. A practical approach is: use a free builder to prototype, then upgrade to a paid plan once you are ready to launch with a custom domain and a credible brand experience.