1-Just as it is haram (act or deed which is prohibited by Allah) to do evil deeds, so too is it not allowed to be means for prohibited things. In this sense, being a means for such a thing holds a person responsible. After all, most of our scholars hold the belief that it is forbidden to do such a thing.

2- However, since you are not directly engaged in the interest transaction, you will not get the same sin because what is haram is to misuse your work. After all, setting up a program in essence is not illicit. Therefore, the program you are going to develop for them is not directly haram. We can compare it to a store hired for an alcohol manufacturer. According to Imamı Azam, it is not forbidden to rent out the store for someone who is going to turn out it to alcohol manufacturing place. From this point, the work itself that you do is not forbidden but rather what is illicit is to use your work wrongly.

3-However, it does not mean that you are totally free of responsibility even if it is not illicit. Helping them in such a matter is at least makrooh (abominable). Makrooh means it is close to haram and it makes you responsible. Consequently, we do not advise you to do such a thing if you are not under an obligation.

4- It is not abominable for you if your work is multi-functional and the people making the interest transactions are going to use your program, that is to say, if your work is not specifically designed for interest purposes.