H2O

What it does

Binary packages

Binary packages are listed for FreeBSD, Homebrew on macOS, RPM distributions including Fedora, RHEL/CentOS and OpenSUSE, and Docker.checked 1 Oct 2026

Dependencies

Building the standalone server requires a C/C++ compiler, CMake, pkg-config, OpenSSL 1.0.2 or later or a compatible TLS stack, and zlib.checked 2 Oct 2026

Deployment

The install guide documents building from source with CMake and lists binary packages for FreeBSD, macOS Homebrew, several RPM distributions, and Docker.checked 2 Oct 2026

Disclosure policy

After acknowledgement, the project uses a 90-day public-disclosure window followed by a possible 14-day grace period.checked 1 Oct 2026

HTTP/2

HTTP/2 support includes dependency- and weight-based prioritization and cache-aware server push.checked 1 Oct 2026

HTTP/2 and HTTP/3

Features include HTTP/2 prioritization and cache-aware server push, plus HTTP/3 Extensible Priorities and a fusion AES-GCM engine for QUIC packet generation.checked 2 Oct 2026

HTTP/3

HTTP/3 support includes Extensible Priorities and a fusion AES-GCM engine for QUIC packet generation.checked 1 Oct 2026

Installation

Source installation requires a C or C++ compiler, CMake, pkg-config, OpenSSL 1.0.2 or later, and zlib.checked 1 Oct 2026

Library

H2O is also available as the libh2o software library.checked 1 Oct 2026

Library use

H2O can also be used as the libh2o software library; building it requires libuv 1.0 or above and OpenSSL 1.0.2 or above.checked 2 Oct 2026

License

The FAQ states that H2O is licensed under the MIT license.checked 2 Oct 2026

Other capabilities

H2O supports static file serving, FastCGI, reverse proxying, mruby scripting, graceful restart, and self-upgrade.checked 2 Oct 2026

Performance

The maker says H2O provides quicker responses with less CPU and memory-bandwidth use than older-generation web servers.checked 2 Oct 2026

Purpose

H2O is an optimized HTTP server supporting HTTP/1.x, HTTP/2, and HTTP/3.checked 2 Oct 2026

Release policy

Since April 2023, H2O has ceased version releases and treats each master-branch commit as stable except features marked experimental.checked 1 Oct 2026

Release status

The install page says H2O ceased releasing versions as of April 2023 and treats each master-branch commit as stable except features marked experimental.checked 2 Oct 2026

Scripting

H2O can be scripted using mruby with Rack-based support.checked 1 Oct 2026

Security

The repository has a security advisories page listing reported vulnerabilities and fixes, and asks users to report vulnerabilities by email.checked 2 Oct 2026

Security reporting

Security issues should be reported privately to [email protected].checked 1 Oct 2026

Support

The FAQ directs users with problems to GitHub issues tagged as FAQ.checked 2 Oct 2026

TLS

TLS features include automated ACME certificate retrieval, session resumption, automatic session-ticket key rollover, and OCSP stapling.checked 2 Oct 2026

Web serving

H2O provides static-file serving with asynchronous I/O, FastCGI and reverse-proxy support.checked 1 Oct 2026