Are you allowed to block ads on YouTube and other sites that require a subscription to watch without ads?

Shalom U'Vracha, Yes, you may block the ads. If the site explicitly writes that they forbid blocking ads on your own and requires a subscription then it is a 'midat chasidut' (going beyond the halachah and observing the spirit of the law) to not block ads without subscribing. Since some of the advertisements may fall short on modesty (tzniut), the midat chasidut would be to pay the site to block the advertisements or not to use the site at all Detailed explanation: If the site doesn't explicitly forbid using the ad blocker then it is definitely permitted. In a case where the site does explicitly forbid using an ad blocker, there are some rabbanim who hold that it would be forbidden to block the ads. Among them is Harav Nir Aviv in his book 'Maase Reshet', (page 192, comment number 197). These rabbanim hold that it is forbidden because you are hurting someone's livelihood and that is included in the prohibition of 'yored leumanut chavero' (loosely translated as demeaning someone's artwork, or harming his revenue), or because you are using someone's possession and this is included in the halachic term 'ze nehene v'zeh chaser' (giving oneself an unfair advantage). See: https://www.yeshiva.org.il/ask/93593 , https://www.yeshiva.org.il/ask/109738 However, there are a few reasons to be lenient in this case: 1. Copyrights: there is a big disagreement amongst the poskim regarding copyrights. If someone writes a book or composes songs does he own them according to the halacha? Many poskim hold that he does, among them Harav Moshe Feinstein in his book, Igrot Moshe, (Orach Chaim, part 4, 40, 19) , Harav Vozner (see Shevet Halevi, part 10, 276). Others hold that one is not halachically considered the owner of his copyrights, see Tzitz Eliezer (part 18, 80), Rav Zalman Nechemia Goldberg, (Techumin, 6). see more about this topic in Y'bia Omer (part 7, Chosen Mishpat, 9), and Maayan Omer (part 10, 4). (However, Harav Shlomo Hirsch wrote to me that in our case here using an internet site is more problematic then using someone's copyrights and it may be forbidden even according to the poskim who permitted using another person's copyrights). 2. Gezel Hagoi (stealing from a non-Jew): we can assume that the owner of the site is not Jewish. According to halacha one is not allowed to steal from a non-Jew. However, some poskim say that it might only be a 'rabbinical decree' (miderabanan) as opposed to a Torah law (mideorayta) see Rashi on Sanhedrin 57, 1 d"h 'Yisroel', who holds that it's forbidden miderabanan because it's a Chilul Hashem, (desecration of G-d's name) . See also Yam Shel Shlomo, Baba Kama, (10, 20). According to Rashi's view, it is possible that in our case it is not forbidden at all since perhaps there is no Chilul Hashem here. 3. Mechila: It is possible that the owners of the site are forgiving of their readers who do this and actually kind of permit one to use the site. After all, even though they say that you cannot use the ad blocker they could surely prevent it's use it if they wanted to or even sue the ad blocking companies. On the other hand, maybe this assumption is not correct because it's possible that they really are not forgiving of this action and forbid using these ad blockers. For other reasons perhaps they don't want to deal with it (stopping ad blockers would involve a lot of time and money). 4. The owners of the site did not forbid the use of the site: The owners of the site probably didn't write explicitly that they do not let you use the site if you block the advertisements-- rather they allow you to use the site but write that you may not block the advertisements. This means that using the site is not considered stealing. Therefore, the problem is just in blocking the advertisements, which is an indirect type of damage. Even without blocking the advertisements you do not have to watch the advertisements. 5. 'Yeush', (or 'giving up'): Some hold that anyone who puts something on the internet is 'mityaesh', meaning that he gives up hope of control because he knows that it's lost to the big cyberworld and he has no way of stopping it's use. According to this psak, one would be allowed to download material from the internet (Harav Dov Lior). Others disagree with this claim (Harav Asher Weiss). 6. Minhag Haolam, (or the 'way of the world'). We might be able to say that the minhag haolam is to be lenient on these issues. we should take into consideration the fact that we see many people do these types of things. The Gemara mentions a few times: "puk chazei mai ama devar"-- 'go out and see how the world deals with this matter'. (Although, one can claim that this is the same sad 'minhag' mentioned in the Gemara (Baba Batra) that most people steal…) Harav Shlomo Hirsch agreed that it is permitted, and part of the answer was based on reasons that he mentioned to me. Additionally I spoke to one of the leading rabbis today Hagaon harav dov lior who also permitted it. In summary; one may block the ads. If the site explicitly writes that they forbid blocking ads on your own and require a subscription then it is a 'midat chasidut' to not block without subscribing. Since some of the advertisements fall short on modesty, the midat chasidut, or going beyond the simple law, would be to pay the site to block the advertisements or not to use the site at all. All the best