For the uniform distribution, the mean value $\mu$ is then $$\begin{equation*} \mu=\langle x\rangle=\frac{1}{2} \end{equation*}$$ while the standard deviation is $$\begin{equation*} \sigma=\sqrt{\langle x^2\rangle-\mu^2}=\frac{1}{\sqrt{12}}=0.2886. \end{equation*}$$