There is a programmatic interface to this applet. Here is an example that converts a list of JD_UTCs to BJD_TDB for alpha Centauri. The RA and Dec are always in decimal hours and the FUNCTION can be utc2bjd, bjd2utc or hjd2bjd. It does not support any observatories, so is only accurate to 20 ms.
This calculator should not be used for targets inside the Solar System. We (and all other online calculators we know of) use a plane wave approximation that is only accurate to 1000 seconds for the Moon, 100 seconds for the Main Asteroid Belt and 5 seconds for the Kuiper Belt. Our source code can, however, deal with this and can be run with a demo license of IDL (not tested on Windows). If you would benefit from an online tool that would work within the Solar System, please email me.
If you have made use of this calculator (or the source code) in a scientific paper, please cite our paper, which contains a more thorough explanation of the various corrections involved in this calculation.