The DMCA could definitely be relevant. It mandates[0] that "No person shall circumvent a technological measure that effectively controls access to a work protec

The DMCA could definitely be relevant. It mandates[0] that "No person shall circumvent a technological measure that effectively controls access to a work protected under this title." IANAL, but one could argue that YouTube (or large parts of it) are protected under copyright law, and that the user agent check is "a technological measure that effectively controls access" to it/them. "(A)to “circumvent a technological measure” means to descramble a scrambled work, to decrypt an encrypted work, or otherwise to avoid, bypass, remove, deactivate, or impair a technological measure, without the authority of the copyright owner; and (B)a technological measure “effectively controls access to a work” if the measure, in the ordinary course of its operation, requires the application of information, or a process or a treatment, with the authority of the copyright owner, to gain access to the work."[1] [0]: (a)(1)(A) https://www.law.cornell.edu/uscode/text/17/1201 https://www.law.cornell.edu/uscode/text/17/1201 [1]: https://www.law.cornell.edu/definitions/uscode.php?def_id=17-USC-423854455-1095614619&term_occur=1 https://www.law.cornell.edu/definitions/uscode.php?def_id=17...