6502 Assembler OnlineAssembly in, machine code out.

Paste 6502 assembly and see each line's address and bytes, the symbol table and a hex dump.
Download the binary, or run it right here and step through it.

Listing & symbolsHex dump & .binRun and debug it

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Your code is assembled and run on your device. Nothing is uploaded.

THREE SIMPLE STEPS

How to use the 6502 Assembler

Paste your code

Type or paste 6502 assembly, or open an .asm file. Labels, constants, .org and data directives are supported.

Assemble

Press Assemble. Errors show their line numbers; the Assembler output tab lists every line's address and bytes and all symbols.

Export or run

Copy the hex dump, download the .bin file, or press Run to execute the code and debug it.

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$1 in free credits for eligible new accounts. No card needed. Generators have separate account and credit requirements. The 6502 emulator is free.

6502 Assembler FAQ

Which syntax does the assembler accept?

Labels with or without a colon, define name value and name = value constants, *= and .org, .byte/dcb, .word, .text, .asciiz and .res, numbers in hex, binary, decimal and character form, arithmetic, and < and > for the low and high byte of an address.

How does it choose zero page or absolute addressing?

A value known to be below $100 when the line is assembled uses the shorter zero-page form. A label defined further down, or a number written with four hex digits such as $00FF, uses the absolute form.

What does the output look like?

A listing with each source line's address and bytes, a symbol table, and a hex dump of 16 bytes per line. The .bin download covers the lowest to the highest assembled address, with gaps filled with zeros.

Which instructions are supported?

All 151 documented NMOS 6502 instructions and every addressing mode, the same instruction set used in classic 6502 books and tutorials.

Is it free and private?

Yes. This online 6502 assembler is free with no sign-up, and your code is assembled in your browser, never uploaded.

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6502 Emulator