I want write simple debugger for one thread.

My idea run and stop thread for execute one asm instruction.
And get registers status.

Whear is looking examples do this ?

if its only 1 asm instruction, then you can use SEH x86; just place an int3 after your instruction.

unless you want to write a fully featured debugger, then you may want to check msdn/docs for windows debugging mechanism.

No.
I dont want write big debugger.

I want writed my small debugger.
For debugging string search\replace small asm code.

Idea print string and show different colors whear is text position now and new changed text copy.

I press key (for example F8 ) and my debugger run one asm command.
And show whear is text position now and new changed text copy.

Because not easy modifi code (after few months) and remember how work logic this asm code in 40 asm lines.

in this case you need a disassembler, a debugger is just a tiny program that can pause/continue execution of debugee's threads.

replacing and/or stepping assembly instructions cant be done by the debugger itself, you need a disassembler.

disassembler is the one that tells the debugger how many bytes is the next instruction to execute and pause the thread.

so you better off using debuggers like olly because it comes with a disassembler.