---------------------------
Level 1
Hints : Title translate to NOT in binary, URL means boolean in 1337

Boolean function NOT basically invert 0 and 1 so :
NOT(1001011110011010100100111001001110010000)
= 0110100001100101011011000110110001101111
Translate with binary code
→ hello
--------------------------
Level 2
Hints : the 1st element of the sequence ("u") is in black font, inspect source code or just select it

This is a variant of the 1, 11, 21, 1211, 111221... sequence
It works better in french where "un" means one, so you would say one "u", one "n", ...
But anyone can figure out that :
u → unu
n → unn
At the end it will give you : unuunnunuunuunnunnunuunnunu
--------------------------
Level 3
Hints : Title tells us there are 5 steps. (the URL 1518 is used later on)

The cipher proceeds like that :

1st step : base64
2nd step : decimal
3rd step : morse
4th step : hex

You should get 4:"-< or 0011010000111010001000100010110100111100
The key "01011000 01001111 01010010" translates "XOR", meaning the last step is a XOR cipher
6th step : 0011010000111010001000100010110100111100 XOR 01011000 01001111 01010010 (or using text value, both works on dcode.fr, the site I linked in the first page hints)
It translates to "lupus"
--------------------------
Level 4
Hints : Title "files - rank" chess terms meaning you should look for letters on specific squares of the chess board (labelled a1, b2, d4, f7,....), see this for more infos.
You would also notice the first 5 letters, they are the only one in caps and have a special effect. They will be used later on.

The squares are given by the fonts (in "fnt.png") and the numbers. The first letter of the font name is the file, the number is the rank.
This requires to recognize fonts (I used very recognizable fonts that can be found in word, paint, photoshop, ....)
This is how the solution should look like : https://radiologie.neocities.org/font%20solution.png
The squares are : f8, b6, a7, c4, g6, c2, c1 and f5
→ xyzxclpng
--------------------------