Compared with what you have

You already have an assembler that works. This page is about what changes if you put asm198x in front of it, and — more usefully — what does not.

What does not change

Your syntax. Every dialect here is somebody else’s assembler. You keep the source you have and name the dialect it is written in; there is no house dialect to convert to. Dialects lists them all.

Your bytes. The point of matching a reference assembler is that the output is the same. Where it is knowingly not, that is written down — see Where we differ.

Your build. asm198x reads a file and writes a file. It has no opinion about your Makefile.

What we measured against

This is the part worth checking rather than believing. Every recorded verdict carries the reference tool’s own version self-report, so the corpus can say exactly which build of which assembler produced the bytes we compare with:

Reference tool	The version we measured against	Instruction sets	Verdicts
acme	This is ACME, release 0.97 (“Zem”), 28 June 2020	1	984
asl	Macro Assembler 1.42 Beta [Bld 309]	14	6112
ca65	ca65 V2.18 - N/A	3	1241
lwasm	lwasm from lwtools 4.25	1	1146
pasmo	PasmoNext v0.1.3 (PC) (C) 2004-2005 Julian Albo	1	2284
rgbasm	rgbasm v1.0.3	2	1125
sjasmplus	SjASMPlus Z80 Cross-Assembler v1.21.0 (https://github.com/z00m128/sjasmplus)	2	556
vasmm68k_mot	vasm 2.0b (c) in 2002-2025 Volker Barthelmann vasm 2.0f (c) in 2002-2026 Volker Barthelmann	1	3392

The version column says what we measured against, not what is current. That distinction is the reason the table can be trusted: a reference tool shipping a new release does not make this page wrong, because it is a record of an observation rather than a claim about the world. Why asm198x has the totals and how the replay works.

What arrives with it

Stated as what this tool does, because that is what we can vouch for:

One binary	Every dialect above, one install, the same interface on macOS, Linux and Windows
fmt	Canonical layout for every dialect, idempotent, and the bytes do not change
disasm	Every dialect, in that dialect’s own syntax, and it reassembles
--prg, --sna, --gb-rom, --exe	The loadable file comes out of the assembler
--message-format=json	Structured results and diagnostics for editors and build scripts
--debug, --sym, --listing	A Debug198x sidecar, a symbol table, an address/bytes/source listing
Multi-file	-I search paths, with each dialect’s own resolution rules — see Projects in more than one file

What this page does not claim

It says nothing about what any other assembler can or cannot do.

That is deliberate. A feature comparison is a claim about software we do not control and do not track, and the moment one of those tools ships, a table like that becomes wrong without anyone touching it — which is exactly the failure the rest of this documentation is built to avoid. Writing “X has no formatter” from memory would be worse still.

So the comparison offered here is the one we can stand behind: these are the tools we measured against, this is the version of each, this is what we produce, and here is every place we knowingly differ. What your current toolchain does, you already know better than we do.