Cheat Engine

[smx]

When i have to do code injections or asm edits where the size of opcodes matter, i always struggle to get the opcode length (bytes) and i have to assemble it somewhere, then look at Bytes column

random example:
chrome.exe+48B23 - 75 06 - jne chrome.exe+48B2B
chrome.exe+48B45 - E9 89FEFFFF - jmp chrome.exe+489D3

Is there a way to tell how many bytes does an opcode require without assembling it?

[Dark Byte]

easiest method is just use the code injection template in the auto assembler.
it figures out the size of the instructions for you. You just have to make sure that nothing jumps inbetween the instruction(s) it's overwriting

But if you do it yourself you'll have to assemble it manually, or don't pick instructions that are affected by their position. (Jumps and calls are affected by their location)

[smx]

I just digged in how the opcodes are encoded/handled and...
I'll stick with the auto assembler then, Thank You

[vergilganesh]

basically two numbers joins to form an opcode..
E9 89FEFFFF consisits of 5 bytes(E9 89 FE FF FF).