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netcode is a simple connection based client/server protocol built on top of UDP.

It has the following features:

  • Encrypted and signed packets
  • Secure client connection with connect tokens
  • Connection based protocol built on top of UDP

and protects your game server from the following attacks:

  • Zombie clients
  • Man in the middle
  • DDoS amplification
  • Packet replay attacks

netcode is stable and production ready.

How does it work?

Please refer to the second half of this whitepaper: Why can't I send UDP packets from a browser?

For a complete technical specification, read the netcode 1.02 standard.

Source Code

This repository holds the reference implementation of netcode in C.

This is the primary implementation of netcode, and is always up to date with the latest features.

Other repositories include:


These people are awesome:

Thanks for your contributions to netcode!


The author of this library is Glenn Fiedler.

Other open source libraries by the same author include: yojimbo and reliable

Glenn is now the founder and CEO of Network Next. Network Next is a radically new way to link networks together. A new internet where networks compete on performance and price to carry your traffic. Check it out at


netcode was generously sponsored by:

And by individual supporters on Patreon. Thank you. You made this possible!


BSD 3-Clause license.