You no longer need a mainframe to learn mainframe assembler.
Today, the Open Mainframe Project is annoucning Gait as a new open source project donated by 21CS. Gait offers students, educators, and developers a practical way to learn assembler, experiment with code, and see how mainframe instructions work—using tools many developers already know.
Explore assembler, instruction by instruction
Gait lets you write and run assembler programs directly in VS Code, then step through them to understand their behavior. You can set breakpoints, move forward and backward through instructions, and inspect or modify registers, memory, the program status word (PSW), and condition codes. A machine-code view shows how instructions are assembled.
The extension supports arithmetic, branching, packed decimal, literals, DSECTs, and multiple CSECTs. Built-in sample programs and reference documentation help new users get started and clarify which instructions are supported, including differences from real mainframe hardware.
Gait gives developers a local environment to build assembler skills without connecting to a mainframe. This can make it easier for students and educators to introduce low-level programming, and for developers to try ideas and better understand mainframe operations.
Part of a broader open source toolkit
Gait joins technologies such as HLASM Language Support, which assists with writing assembler code, and Zowe, which supports modern development workflows and connectivity to z/OS environments. Together, these tools can help developers move from learning and local experimentation to working with mainframe systems.
The project welcomes community contributions, bug reports, and feature suggestions as its capabilities grow.
Introducing Gait at GS UK Forge
Gait is being introduced in conjunction with GS UK Forge Conference 2026, taking place November 2–5 in Whittlebury, London. 21CS will highlight the project and its potential to expand access to mainframe assembler development in a conference keynote. The event also includes an Open Mainframe Project track focused on open source innovation and modern mainframe technologies.
Learn more about Gait and find ways to explore or contribute through the Open Mainframe Project.
