We were not expecting this, but it's actually a smart move from Blizzard! A new Deck Builder has been released on the official Hearthstone website, and it's pretty well done.
It is available for free in English and many other languages here, and you can create decks in both Standard and Wild modes.
If some options are missing to make it even more accurate and intuitive, it is easy to handle whether you are a beginner or an expert. Details on each card are given, and above all, it shows all the cards that can be linked together.
For example, for Jan'alai, you can see directly Ragnaros the Firelord and its Related Cards. This is especially useful for cards like Ysera since all Dream Cards are shown.
If an experienced player can have them all in mind, the less experienced players will find significant help there.
Decks can be easily shared, and you can either copy the deck code, in order to import it into the game, or copy URL to share it online!