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Miracle

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What Miracle is

Miracle is free JavaScript software that emulates the Sega Master System inside a web browser. You can open a ROM file or choose a listed game without installing a separate desktop application. The interface includes Play, Pause, Step, Step Over, Step Out, Reset, and Open ROM controls. Keyboard input uses the cursor keys together with Z or Y and X; P pauses the emulator and R resets it. Pressing Backspace opens the built-in debugger. Miracle is credited to Matt Godbolt and builds on JSSpeccy, which itself is based on Fuse. The source code is publicly available, and the maker describes the project as licensed under the GNU General Public License version 3 or later. The project documentation says building requires Node.js 18 or newer. Its reported CPU test results show 1,329 of 1,356 FUSE Z80 tests passing, with 27 skipped because they cover behavior considered unrelated to Sega Master System emulation. The maker provides the software without warranty.

Who it suits

It suits people who want to play or inspect Sega Master System ROMs in a browser. Developers can also examine the source and use its debugger or build process.

What it does well

  • Runs entirely inside a web browser
  • Loads local ROM files or listed games
  • Built-in debugger with stepping controls
  • Source code is publicly available
  • Free under GPL version 3 or later

What to know first

  • Requires ROM files for games not listed
  • Building requires Node.js 18 or later
  • Maker provides no warranty

Getting started

  1. Open https://miracle.xania.org/ in a web browser
  2. Select a game listed on the page or open a ROM file
  3. Use the cursor keys, Z/Y, and X for controls
  4. Press P to pause or R to reset
  5. Press Backspace to open the debugger

Verdict

Miracle offers browser-based Sega Master System emulation with ROM loading, keyboard controls, and debugging tools. Its public source and GPL license also support users interested in examining or building the project.

Questions

What does Miracle emulate?

Miracle emulates the Sega Master System using JavaScript in a browser.

How much does Miracle cost?

Miracle is free, with a free plan.

Can I load my own games?

Yes. The browser interface lets you open a ROM file, and it also offers a list of games.

Is Miracle open source?

Yes. Source code is publicly available, and the maker describes the software as GPL version 3 or later.

Who made Miracle?

The page credits Matt Godbolt. The project is based on JSSpeccy by Matt Westcott and Fuse by Philip Kendall and others.

Facts from Miracle's own pages

Build requirement
The project README says building requires Node.js version 18 or later. · github.com, 7 Oct 2026
Controls
The cursor keys and Z/Y and X control the emulator; P pauses it and R resets it. · miracle.xania.org, 7 Oct 2026
CPU test suite
The project README reports 1,329 of 1,356 FUSE Z80 CPU tests passing and says the 27 skipped tests cover behaviors not relevant to SMS emulation. · github.com, 7 Oct 2026
Credits
Miracle is based on JSSpeccy by Matt Westcott, which in turn is based on Fuse by Philip Kendall and others. · miracle.xania.org, 7 Oct 2026
Debugger
The emulator includes a built-in debugger that opens with Backspace. · miracle.xania.org, 7 Oct 2026
Debugger controls
The interface includes play, pause, step, step over, step out, reset, and open ROM controls. · miracle.xania.org, 7 Oct 2026
Emulation tests
The repository says 1,329 of 1,356 FUSE Z80 CPU tests pass and identifies 27 skipped tests as covering undocumented behavior not relevant to SMS emulation. · github.com, 7 Oct 2026
Emulator controls
The interface provides Play, Pause, Step, Step Over, Step Out, and Reset controls. · miracle.xania.org, 7 Oct 2026
License
The maker describes Miracle as free software under the GNU General Public License, version 3 or later. · miracle.xania.org, 7 Oct 2026
Maker
The page credits Matt Godbolt as the maker. · miracle.xania.org, 7 Oct 2026
Platform
The product is described as running totally inside a browser. · miracle.xania.org, 7 Oct 2026
Product
Miracle is a JavaScript Sega Master System emulator that runs inside a browser. · miracle.xania.org, 7 Oct 2026
Project lineage
Miracle is based on JSSpeccy, which in turn is based on Fuse. · miracle.xania.org, 7 Oct 2026
Purpose
Miracle is a JavaScript Sega Master System emulator that runs in a browser. · miracle.xania.org, 7 Oct 2026
ROM loading
Users can open a ROM file in the browser or select a listed game. · miracle.xania.org, 7 Oct 2026
ROMs
The page lets users open a ROM file or select a listed game. · miracle.xania.org, 7 Oct 2026
Source code
The public repository says Miracle can be tried at miracle.xania.org and documents building it with Node.js v18 or later. · github.com, 7 Oct 2026
Warranty
The maker states that the program is provided without warranty, including implied warranties of merchantability or fitness for a particular purpose. · miracle.xania.org, 7 Oct 2026

Where Miracle stands on Freedom251

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