Piston Assembler
JavaScript Assembly CoffeeScript
Latest commit 5ade584 Dec 16, 2012 @tpisto Update README.md


Piston X86-64 Assembler

Piston X86-64 Assembler (PASM) is NASM syntax based symbolic machine code compiler for X86-64 architecture - fully working in browser and in Node.js based environments. Test live demo


  • X86-64 opcodes
  • NASM syntax
  • 16,32,64 bit modes
  • R8-R13 registers
  • SIB, MODR/M, RIP addressing
  • labels, expressions
  • testing framework


  • It works <-- We are here
  • Floating point instructions, rep, segment prefixes, MMX, macros, ...

Download and install

Releases are available for download from GitHub.

Alternatively, you can install using Node Package Manager (npm):

npm install pasm


pasm simple.asm

In the Browser

So far its been tested in FF12, Chrome 23 and Safari 6. Usage:

<script type="text/javascript" src="pasm.min.js"></script>
<script type="text/javascript">

    // Define where to show errors
    myError = function(err, line) {
      console.log('Error:' + err + ' in line ' + line);
    window.Opcode.error = myError;
    pasm.parseError = myError;

    // Parse assembler code
    var hexString = pasm.parse('mov ax, 0x4c00');