Builders on Ethereum are concerned by centralization, otherwise they wouldn't build on Ethereum right? Still, most Dapps today rely on trusted 3rd party nodes. We need to change this. Over the past months, we have built Fether, a wallet based on a light client. We will show in this presentation the lessons learned and share our takeaways on how to best build an application on top of a light client. We will present light.js, the library we've built to enable builders to use good practice and have a Dapp that is truly decentralized.