From the git repo:

    webMARS is a browser implementation of MARS MIPS 4.5: editor, assembler, simulator, help system, and classic MARS tools in a single web UI.

    Overview

    - Single-page IDE for editing, assembling, running, stepping, backstepping, and debugging MIPS programs.
    
    - Multi-window desktop/mobile UI with registers, text/data segments, labels, messages, Run I/O, and tool windows.
    
    - Built-in help system with localized pages and embedded reference material.
    
    - Persistent browser workspace for files, session restore, settings, and tool state.
    
    - Single JavaScript assembler and simulator core, with no native runtime dependency.

And from [0]:

    MARS is a lightweight interactive development environment for programming in MIPS assembly language, intended for educational-level use with Patterson and Hennessy's Computer Organization and Design.

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To run the demo program:

1. Run > Compile

1a. In the popup window select 'Open ASM as new file'

2. Run > Assemble, context will change to the 'Execute' tab.

3. Click the little 'Go' button near top-center.

4. ???

5. Profit!

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[0] https://computerscience.missouristate.edu/mars-mips-simulato...

Very nifty! Looks amazing ... :) I love the Netbeans ish style UI

Check my git:

https://github.com/codigoavulso/webMARS/

TY!