: A highly-regarded free, open-source Modbus master simulator.

: A free trial version is available that offers full functionality but is limited to sending and receiving only six request messages . Once this limit is reached, the application must be restarted to reset the counter. Free & Open-Source Alternatives

The most critical argument against using unauthorized license keys in an industrial setting is the issue of cybersecurity. Unlike consumer software, industrial control systems (ICS) often manage critical infrastructure, manufacturing lines, and utility networks. When a user downloads a cracked executable or uses a keygen from a "top" search result, they are essentially inviting unverified code into their operational environment. Malicious actors frequently embed malware, ransomware, or backdoors into cracked software. A compromised Modbus master tool could silently inject false commands into a network, causing physical damage to equipment, or provide a gateway for attackers to access the broader control network. In an era where industrial cyberattacks are increasingly common, the risk of compromising a facility’s safety for the price of a software license is an unacceptable gamble.

If you only need basic testing and don't want to purchase a license, there are several reputable free or open-source alternatives: QModMaster: