\documentclass[tikz,convert={outfile=\jobname.svg}]{standalone}
%\usetikzlibrary{...}% tikz package already loaded by 'tikz' option
\tikzset{dot/.style={draw,shape=circle,fill=black,scale=0.5}}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}[scale=1, very thick]
	\draw (0,0) -- (0,1) -- (1,1) -- (1,0) -- cycle;
	\draw [red] (0,0) -- (1,1);
	\node [dot] at (0,0) {};
	\node [dot] at (0,1) {};
	\node [dot] at (1,1) {};
	\node [dot] at (1,0) {};
	
	\node at (-0.1,-0.1) {};
	\node at (1.1,1.1) {};
\end{tikzpicture}
\end{document}
