Custom Build

This section details how to build custom build a Merlin Agent using the Make file.

NOTE: Merlin is distributed with pre-compiled agent binaries for all major platforms in the data/bin directory.


The provided Make file can be used to build a new agent from source. It is recommended that you first use go get to pull a copy of the Merlin source code to the host. Move into the Merlin root directory where the Make file is located.

  • Windows agent: make windows
  • Linux agent: make linux
  • macOS agent: make darwin
  • MIPS agent: make mips
  • ARM agent: make arm


Use the provided Make file to build a Merlin Agent with hard coded values. This removes the need for an operator to use commandline arguments and allows the Agent to simply be executed. The table below shows configurable compile options

Build Options
Option Description Notes
HOST HTTP Host header same as -host commandline flag
JA3 JA3 signature string (not the MD5 hash). Overrides -proto flag same as -ja3 commandline flag
KILLDATE The date, as a Unix EPOCH timestamp, that the agent will quit running same as -killdate commandline flag
MAXRETRY The maximum amount of failed checkins before the agent will quit running same as -maxretry commandline flag
PADDING The maximum amount of data that will be randomly selected and appended to every message same as -padding commandline flag
PROTO Protocol for the agent to connect with [https (HTTP/1.1), http (HTTP/1.1 Clear-Text), h2 (HTTP/2), h2c (HTTP/2 Clear-Text), http3 (QUIC or HTTP/3.0)] (default ‘h2’) same as -proto commandline flag
PROXY Hardcoded proxy to use for http/1.1 traffic only that will override host configuration same as -proxy commandline flag
PSK Pre-Shared Key used to encrypt initial communications (default “merlin”) same as -psk commandline flag
SKEW Amount of skew, or variance, between agent checkins same as -skew commandline flag
SLEEP The amount of time the Agent will sleep between checkins Must use golang time notation (e.g., 10s for ten seconds) same as -sleep command line flag
URL Full URL for agent to connect to (default “”) same as the -url commandline flag
USERAGENT The HTTP User-Agent header string that Agent will use while sending traffic same sas the -useragent commandline flag

An example of creating a new Linux HTTP agent that is using domain fronting through using a PSK of SecurePassword1:

make linux URL= PROTO=https PSK=SecurePassword1

Windows Agent

The Windows Merlin Agent executable is compiled as a GUI application instead of console application. The Merlin Agent does not have a GUI component. The reason this is used is so that the Merlin Agent window disappears after it is executed. This behavior is intentional so that the user will not see the application window. This is done with the LDFLAGS when building the agent using the -H=windowsgui option as shown here

This causes problems when a user WANTS to see the Merlin Agent verbose or debug output. To view Merlin verbose/debug output, use the Makefile windows-debug target (e.g., make windows-debug)


The Merlin agent and server can be cross-compiled to any operating system or architecture. A list of golang supported operating systems and architectures can be found here:

Supported Platforms
android arm
darwin 386
darwin amd64
darwin arm
darwin arm64
dragonfly amd64
freebsd 386
freebsd amd64
freebsd arm
linux 386
linux amd64
linux arm
linux arm64
linux ppc64
linux ppc64le
linux mips
linux mipsle
linux mips64
linux mips64le
netbsd 386
netbsd amd64
netbsd arm
openbsd 386
openbsd amd64
openbsd arm
plan9 386
plan9 amd64
solaris amd64
windows 386
windows amd64


The gomobile library can be used to compile for Android and iOS:

These instructions can be followed to compile for Android

  • Install Android SDK:
  • Install gomobile:
    go get
  • Initialize gomobile:
    bin\gomobile init -ndk=C:\Users\[username]\AppData\Local\Android\Sdk\ndk-bundle
  • Build the APK:
    bin\gomobile build -target=android merlinagent