KCP vs quic-go
Which should you use? A side-by-side look at what each one does, who it suits, what it costs, how hard it is to set up, and where each falls short.
Open source · MIT
A small C library that adds fast, reliable retransmission on top of UDP.
Open source · MIT
A Go library implementing the QUIC transport protocol and HTTP/3, with no cgo dependency.
The short answer
Choose KCP if you need…
- Developers building their own UDP-based protocol who need reliable delivery
- Projects that need lower latency for small, time-sensitive messages
- Developers embedding a protocol stack in C or porting it to other languages
- Teams building games or real-time media transport that can accept extra bandwidth use
Choose quic-go if you need…
- Go developers building servers or clients that need QUIC or HTTP/3
- Teams writing network tools, proxies, or tunnels in Go
- Projects that want to use the qlog format for protocol debugging
- Developers who need WebTransport, CONNECT-UDP, or CONNECT-IP through the related quic-go projects
Side-by-side
| KCP | quic-go | |
|---|---|---|
| Type | Library | Library |
| Price | Free and open source | Free and open source |
| Licence | MIT | MIT |
| GitHub stars | 17k | 11.8k |
| Setup difficulty | Advanced | Advanced |
| How you get it | Clone and build from source | Install with a package manager |
| Main language | C | Go |
| Last code update | 5 months ago | 4 days ago |
What each one is
KCP
KCP is a networking algorithm written in C that makes UDP packets arrive reliably, by resending lost data and acknowledging receipt. It trades some extra bandwidth for lower latency than TCP, according to the README. It does not send or receive packets itself; the program using it supplies the UDP send and receive code and the clock.
quic-go
quic-go is a Go library that implements QUIC, the transport protocol (RFC 9000, 9001, 9002) that underlies HTTP/3, along with related extensions such as datagrams and qlog event logging. Developers use it to build QUIC clients and servers inside Go programs rather than running it as a standalone application. The README describes it as pure Go.
Best for
KCP
- Developers building their own UDP-based protocol who need reliable delivery
- Projects that need lower latency for small, time-sensitive messages
- Developers embedding a protocol stack in C or porting it to other languages
- Teams building games or real-time media transport that can accept extra bandwidth use
quic-go
- Go developers building servers or clients that need QUIC or HTTP/3
- Teams writing network tools, proxies, or tunnels in Go
- Projects that want to use the qlog format for protocol debugging
- Developers who need WebTransport, CONNECT-UDP, or CONNECT-IP through the related quic-go projects
Strengths
KCP
- Small footprint: the README says the whole protocol is two source files, ikcp.h and ikcp.c
- Does no system calls internally and takes the clock from the caller, which makes it easy to fit into existing event loops
- Many ports exist in other languages (Go, Rust, C#, Java, Python), as listed in the README
quic-go
- Listed as used by several known projects, including Caddy, Traefik, and syncthing, per the README table
- Covers many QUIC and HTTP/3 specifications and has a documented FIPS 140-3 mode for Go 1.26+
- Includes fuzzing and code coverage badges in the README, indicating active testing
Not ideal for
KCP
- People who just want a finished app or tool; KCP is a building block with no user interface
- Projects where bandwidth is tight, since the README says it wastes 10%-20% more bandwidth than TCP
- Anyone unwilling to write the UDP send/receive glue and call update in a loop
quic-go
- People who want a ready-to-run app rather than code to integrate: the project is a library, and the README does not present a standalone program
- Developers not working in Go, since the implementation is Go-only
- Readers who need an explanation of QUIC itself: the README points to the RFCs and quic-go.net docs for that
Trade-offs
KCP
- Uses more bandwidth than TCP by design, per the README's 10%-20% figure
- Does not handle packet transmission, MTU discovery, or encryption; those are the caller's job, with encryption covered only by a linked wiki page
- Requires careful integration (calling update, input, and send correctly), so it is not plug-and-play
quic-go
- Integration requires writing Go code, so it is not useful to someone who only wants to run a tool
- The README does not give performance benchmarks, so claims about speed cannot be checked from this text
- Some supported specifications are drafts (for example, the stream reset draft versions), which may change
Getting started
KCP
Clone the repository
git clone https://github.com/skywind3000/kcpFrequently asked questions
What is the difference between KCP and quic-go?
KCP: A small C library that adds fast, reliable retransmission on top of UDP. quic-go: A Go library implementing the QUIC transport protocol and HTTP/3, with no cgo dependency. KCP suits developers building their own udp-based protocol who need reliable delivery, while quic-go suits go developers building servers or clients that need quic or http/3.
Are KCP and quic-go free?
KCP: Free and open source. quic-go: Free and open source.
Is KCP or quic-go more popular?
KCP has more GitHub stars (17k) than quic-go (11.8k). Popularity isn't the same as fit — check which one matches your use case above.
Built from our catalogue entries for both products: open-source details come from each project's README (AI-assisted, refreshed weekly) and GitHub data; AI-tool details are editorial. Spotted something wrong? Let us know from either product's page.