Online Full — Z80 Disassembler

The online Z80 disassembler is a testament to the enduring legacy of the Z80 CPU and the creativity of the retrocomputing community. It transforms the arcane chore of manual opcode decoding into an interactive, educational, and often joyful experience. Whether you are patching a classic game, analyzing a bootleg arcade board, or simply learning how your childhood computer worked, these web-based tools provide a frictionless entry point into the world of reverse engineering. While they cannot replace the depth of professional offline suites, their accessibility, cross-platform nature, and growing feature sets make them indispensable for hobbyists and digital archaeologists alike. In an era where preserving and understanding vintage software is increasingly urgent, the online Z80 disassembler is a powerful shovel in the dig kit of computing history.

I can’t post directly to forums or social media for you, but here’s a ready-to-copy forum post/reply you can use when asking for a full-featured Z80 disassembler online.

Title: Looking for a full Z80 disassembler online (not just a limited web demo)

Post:

Does anyone know a fully-featured online Z80 disassembler that handles:

I’ve tried the small ones on GitHub Pages, but they usually miss undocumented instructions or only work for tiny code snippets.

Ideally something like z80dasm (command-line) but accessible in a browser.

So far the closest I’ve found:

Does anyone know a better full online tool? Or a way to run z80dasm in a browser (WASM, JS port)? z80 disassembler online full

Thanks!

If you want just the two best online full-featured options to check out right now:

Finding a high-quality "full" online Z80 disassembler is a common request for retro computing enthusiasts working on ZX Spectrum, Amstrad CPC, or TI-84 calculator projects. Many web-based tools are lightweight, but a few stand out for their features and community recognition. Highly Rated Online Z80 Disassemblers

Several platforms offer robust disassembly directly in the browser:

Ghidra. 2023. Available online: https://ghidra-sre.org/ (accessed on 25 September 2023). Binary Ninja

Binary Ninja Cloud is our free, online reverse engineering tool. It supports a number of great features. Binary Ninja

Assuming you won't/can't/don't want to use WinDbg to analyze, another options is to submit it online to be analyzed for you.

The Online Disassembler (onlinedisassembler.com) is frequently cited by the reverse engineering community. It supports multiple architectures including the Z80 and allows you to upload binary files for interactive analysis. The online Z80 disassembler is a testament to

David Gom's Z80 Disassembler is a classic "browser-based" tool. Although the original site has experienced downtime, it is still accessible via the Internet Archive. It was noted for being extremely fast, handling large programs like zStart 1.1 in under a second.

Binary Ninja Cloud provides a high-level, free online reverse engineering platform. While it is a modern general-purpose tool, it has excellent Z80 support with advanced features like control flow graphs and lifting to intermediate languages.

ClrHome's Z80 Assembler/Disassembler is another popular online choice, particularly for TI-83 and Spectrum series development. Comparison of Features Key Strengths Online Disassembler Broad architecture support, interactive UI Quick file analysis without installation Binary Ninja Cloud Control flow graphs, modern UI, deep analysis Serious reverse engineering projects David Gom (Archived) Pure speed, lightweight engine Fast-paced coding sessions ClrHome Built-in editor and assembler Integrated dev for specific retro targets Notable "Smart" & Pro-Level Alternatives

If online tools feel too limited for your project, experts often point toward these more powerful (but downloadable) solutions:

Ghidra: An NSA-developed, free, and open-source suite. It is one of the most powerful options available today, capable of turning Z80 assembly into readable pseudo-C code to help you understand complex logic.

z80-smart-disassembler: A specialized tool on GitHub designed to take the "effort" out of reversing. It automatically identifies and labels strings and data areas, which is a major time-saver for large binaries.

IDA Pro (Free version 3.7): While dated and no longer officially distributed, this specific version of IDA supports Z80 and is still praised for its high-level analysis capabilities.

💡 Pro-Tip: When using online disassemblers, ensure you know your file's load address (the memory location where the code starts). Many tools will fail to produce correct labels or jumps if the origin address is set incorrectly. Title: Looking for a full Z80 disassembler online

What system is the code for (e.g., ZX Spectrum, TI-83, Amstrad)?

Are you disassembling a small snippet or a full ROM/snapshot? Do you need to reassemble the code afterward?

Ghidra. 2023. Available online: https://ghidra-sre.org/ (accessed on 25 September 2023). Binary Ninja

Binary Ninja Cloud is our free, online reverse engineering tool. It supports a number of great features. Binary Ninja

Assuming you won't/can't/don't want to use WinDbg to analyze, another options is to submit it online to be analyzed for you. JEB decompiler

A Z80 disassembler converts Zilog Z80 machine code (binary) into human-readable assembly instructions. An online full Z80 disassembler provides a web interface where you can paste or upload binary/hex, view decoded instructions, follow code flow, and often get features like labels, symbol support, and export.

Given that powerful offline disassemblers like z80dasm, Radare2, or Ghidra exist, why would a developer choose a browser-based tool?

If you prefer offline tools, z80dasm and z80ex are simple command-line disassemblers; combine with objdump-like frontends or custom scripts for labeling and formatting.

The Z80 has 252 root opcodes. A partial disassembler will mishandle ED and CB prefix pages. A full tool correctly decodes LDIR, CPIR, RLC (IX+5), and the exotic IN0/OUT0 instructions found in some embedded Z80s.

There are several reasons to use a Z80 disassembler: