  In this work, we introduce a bottom-up $F(R)$ gravity reconstruction
technique, in which we fix the observational indices and we seek for the $F(R)$
gravity which may realize them. Particularly, as an exemplification of our
method, we shall assume that the scalar-to-tensor ratio has a specific form,
and from it we shall reconstruct the $F(R)$ gravity that may realize it,
focusing on special values of the parameters in order to obtain analytical
results. The observational indices we study are compatible with the latest
observational data, and we discuss how the functional form of the observational
indices may affect the viability of the model.
