What makes a serve legal?

Under Law 9 of the BWF Laws of Badminton, a correct serve needs all of these:

• Position: server and receiver stand in diagonally opposite service courts, not touching the lines of those courts.
• Feet: part of both feet of the server and the receiver stays on the floor, stationary, from the start of the serve until the shuttle is hit.
• No delay: neither side unduly delays the serve once both are ready. Once the server's backward swing is complete, any delay before the forward swing counts as undue delay.
• Release and contact: the server releases the shuttle without adding spin, and the racket first hits the base (cork) of the shuttle.
• Height: the whole shuttle is below 1.15 m from the floor when it's hit.
• Continuous swing: once the forward swing starts, the racket keeps moving forward until the shuttle is hit.
• Flight: the shuttle travels upwards off the racket, over the net, and would land in the receiver's service court (lines count as in).
• Don't miss: missing the shuttle when trying to serve is a fault.

The serve starts with the first forward movement of the racket head. The server must not serve before the receiver is ready, but a receiver who tries to return it is treated as ready.

Some events use the BWF's alternative service law instead of the 1.15 m rule: the whole shuttle below the server's waist (level with the lowest rib) and the racket shaft and head pointing downwards at contact.