h2load - HTTP/2 benchmarking tool - HOW-TO

h2load(1) is benchmarking tool for HTTP/2 and HTTP/1.1. It supports SSL/TLS and clear text for all supported protocols.

Compiling from source

h2load is compiled alongside nghttp2 and requires that the --enable-app flag is passed to ./configure and required dependencies are available during compilation. For details on compiling, see nghttp2: Building from Git.

Basic Usage

In order to set benchmark settings, specify following 3 options.


The number of total requests. Default: 1


The number of concurrent clients. Default: 1


The max concurrent streams to issue per client. Default: 1

For SSL/TLS connection, the protocol will be negotiated via ALPN. You can set specific protocols in --alpn-list option. For cleartext connection, the default protocol is HTTP/2. To change the protocol in cleartext connection, use --no-tls-proto option. For convenience, --h1 option forces HTTP/1.1 for both cleartext and SSL/TLS connections.

Here is a command-line to perform benchmark to URI https://localhost using total 100000 requests, 100 concurrent clients and 10 max concurrent streams:

$ h2load -n100000 -c100 -m10 https://localhost

The benchmarking result looks like this:

finished in 7.08s, 141164.80 req/s, 555.33MB/s
requests: 1000000 total, 1000000 started, 1000000 done, 1000000 succeeded, 0 failed, 0 errored, 0 timeout
status codes: 1000000 2xx, 0 3xx, 0 4xx, 0 5xx
traffic: 4125025824 bytes total, 11023424 bytes headers (space savings 93.07%), 4096000000 bytes data
                     min         max         mean         sd        +/- sd
time for request:    15.31ms    146.85ms     69.78ms      9.26ms    92.43%
time for connect:     1.08ms     25.04ms     10.71ms      9.80ms    64.00%
time to 1st byte:    25.36ms    184.96ms     79.11ms     53.97ms    78.00%
req/s (client)  :    1412.04     1447.84     1426.52       10.57    63.00%

See the h2load manual page OUTPUT section for the explanation of the above numbers.

Timing-based load-testing

As of v1.26.0, h2load supports timing-based load-testing. This method performs load-testing in terms of a given duration instead of a pre-defined number of requests. The new option --duration specifies how long the load-testing takes. For example, --duration=10 makes h2load perform load-testing against a server for 10 seconds. You can also specify a “warming-up” period with --warm-up-time. If --duration is used, -n option is ignored.

The following command performs load-testing for 10 seconds after 5 seconds warming up period:

$ h2load -c100 -m100 --duration=10 --warm-up-time=5 https://localhost

Flow Control

HTTP/2 has flow control and it may affect benchmarking results. By default, h2load uses large enough flow control window, which effectively disables flow control. To adjust receiver flow control window size, there are following options:


Sets the stream level initial window size to (2**<N>)-1.


Sets the connection level initial window size to (2**<N>)-1.


Sometimes benchmarking client itself becomes a bottleneck. To remedy this situation, use -t option to specify the number of native thread to use.


The number of native threads. Default: 1

Selecting protocol for clear text

By default, if http:// URI is given, HTTP/2 protocol is used. To change the protocol to use for clear text, use -p option.

Multiple URIs

If multiple URIs are specified, they are used in round robin manner.


Please note that h2load uses scheme, host and port in the first URI and ignores those parts in the rest of the URIs.

UNIX domain socket

To request against UNIX domain socket, use --base-uri, and specify unix: followed by the path to UNIX domain socket. For example, if UNIX domain socket is /tmp/nghttpx.sock, use --base-uri=unix:/tmp/nghttpx.sock. h2load uses scheme, host and port in the first URI in command-line or input file.


h2load supports HTTP/3 if it is built with HTTP/3 enabled. HTTP/3 support is experimental.

In order to send HTTP/3 request, specify h3 to --alpn-list.