OK. Have a nice day!!

No. There is no simple way of evaluating CBS estimation.

Many thanks Tian. And the last question, do quickCBS calculate the error of the CBS estimation?

ORCA itself directly supports basis set extrapolation via "extrapolation" keyword, therefore I don't plan to make quickCBS support ORCA.
For example, "! CCSD(T) Extrapolate(2/3) tightSCF" will automatically calculate CCSD(T)/CBS energy by cc-pVDZ->cc-pVTZ extrapolation.

Many thanks!!! And do you will have soon support for ORCA outputs?

You should use an appropriate level to optimize the geometry, commonly DFT with a 3-zeta quality basis set is adquate. For organic systems, usually you can use such as B3LYP/def-TZVP to optimize the geometry. I cannot give you detailed advice without information of your system and your computational resource.

Dear Tian,

you have a kindly way to get the CBS limit from CCSD(T) single point calculations, but you don't talk about the starting geometry you need for this task. Do you have a preferred choice?

Thanks in advance,
Antonio