Typo at https://github.com/ISSOtm/gb-asm-tutorial/blob/3176e9da0590a2b92f390fc9db94fd31a58806e4/src/hello-world.html#L186.
It should be FontTilesEnd.

"Another way to prove it is to take any byte, for example 70, and adding 255 to it. This gives 335"
335 should be 325

I made a little checkbox list in case you want to fix these. If you disagree, feel free to just ignore :-)

Index:

• "if you're just a passionate, too". Using "passionate" this way sounds a bit odd to my ear. Maybe "enthusiast" instead?
• "such a small, constrained hardware". "hardware" sounds weird to me. Maybe "device"?
• Personally, I don't really think you need screenshot proof. It sounds a bit defensive.
• You might want to put a link to the repo as a footer on each page. Even better if you can add a link to github issues with a link to that page automatically (I assume that's possible.)

What is Game Boy?

• "These consoles's" looks odd. Maybe "Their successor"?
• Might be nice to have wikipedia links for the consoles you mention.
• "What is what?" doesn't make sense to me. "What are the differences?" sounds better.
• There are a lot of parentheticals here, which I find a bit hard to read. If it's important, I'd suggest making it part of the sentence proper. If it's just extra information, maybe make it a footnote.
• What does "voluntary wave" mean? Searching finds a bunch of references to gameboy docs, but not much else.

Basic Concepts

• "non-integers are stored as int1*10^int2" This doesn't really make sense to me. What are int1 and int2 in this example? And what do you mean by non-integers, floating point numbers?
• Might want to mention two's complement in this section.
• "but also one drawback" you mean that you can't tell the difference between code and data? The way you've written it makes it sound like there's something else.

Tools

• Provide links to the emulators!

At line with label Start getting syntax error. Copied and pasted code from site to make sure everything is the same.
main - Copy.zip

WRAM is the console's work RAM. It's on the

https://eldred.fr/gb-asm-tutorial/memories.html

Notice also that sp is decremented after each push, which essentially means that the stack is placed at the end of RAM, rather than at the beginning (this is called an "ascending" stack).

I'd call this a descending stack. This sounds like a mistake to me. Could you verify?

From https://github.com/ISSOtm/gb-asm-tutorial/blob/master/src/arithmetics.html#L97
In

    ld a, 42

    cp 10 ; 42 - 10 = 32,  C reset (42 >= 10), Z reset (42 != 10)
    ; Notice how you can chain comparisons? That comes in handy at times
--> cp 57 ; 42 - 57 = 241, C set   (42 < 10) , Z reset (42 != 10)
    cp 42 ; 42 - 42 = 0,   C reset (42 >= 42), Z set   (42 == 42)

Shouldn't it be

cp 57 ; 42 - 57 = 241, C set   (42 < 57) , Z reset (42 != 57)

?

; Point hl to the stack, with a signed 8-bit offset
ld hl, sp+4

8-bit?

"The BGP register is split into 4 groups of 2 bytes each."
bytes should be bits here

http://marc.rawer.de/Gameboy/Docs/GBCPUman.pdf
http://www.codeslinger.co.uk/pages/projects/gameboy/hardware.html

The supported flag registers are only:

Z - Zero Flag (a-b = 0)
N - Subtract Flag (used for DAA instructions checking if subtraction was used)
H - Half Carry Flag (carry occurred in first 4 bits)
C - Carry Flag ( A < b)

I am not sure about information on this line; specifically, the sections marked by "Note"s.

Any help, probably from emulator developers, would be appreciated.