  What is the origin of nuclear clustering and how does it emerge from the
nuclear interaction? While there is ample experimental evidence for this
phenomenon, its theoretical characterization directly from nucleons as degrees
of freedom remains a challenge, making it difficult to improve nuclear forces
using clustering observables. In this work, a simple ratio of energies based on
effective scale arguments is proposed to assess the quality of nuclear forces
on alpha clustering (${ {}^{4}\text{He} }$) in bound and narrow ground-state
nuclei. The proposed clustering ratio is parameter-free and correctly identify
basic alpha clustering features in light nuclei. It is found that in nuclei
ranging from ${ {}^{6}\text{Li} }$ to ${ {}^{14}\text{C} }$, state-of-the-art
\textit{ab initio} nuclear forces underestimate the degree of alpha clustering
in key nuclei such as ${ {}^{8}\text{Be} }$ and ${ {}^{12}\text{C} }$.
Stringent constraints on binding energies are then provided by back-propagating
10\% relative uncertainties on the experimental clustering ratios using a
parallel Markov chain Monte Carlo algorithm. It is demonstrated that the
binding energies of the nuclei $^{6,7}$Li, $^7$Be, $^{10,11}$B, and $^{11}$C
need to be obtained within tens of keV precision by nuclear forces to ensure a
proper reproduction of basic alpha clustering features in light nuclei. This
study provides a new and practical path to guide future optimizations of
nuclear forces with a potential impact for medium-mass nuclei.
