The study identifies RIP1 kinase as a specific target of necrostatins, a class of small-molecule inhibitors of necroptosis. Necroptosis is a regulated form of cell death that shares features with unregulated necrosis. Necrostatin-1 (Nec-1) and other necrostatins inhibit RIP1 kinase activity, which is essential for necroptosis. The study shows that necrostatins, including Nec-1, Nec-3, and Nec-5, target RIP1 kinase in the necroptosis pathway, though through different mechanisms. RIP1 kinase is a key upstream kinase involved in necroptosis activation. The study also demonstrates that necrostatins inhibit RIP1 kinase activity in vitro, and this activity correlates with their ability to inhibit necroptotic cell death. The results suggest that necrostatins are first-in-class inhibitors of RIP1 kinase, offering a potential therapeutic approach for diseases involving necrotic tissue injury. The study further identifies that RIP1 autophosphorylation sites, including Ser14/15, Ser20, Ser161, and Ser166, are involved in RIP1 kinase activity. The T-loop of RIP1 is critical for necroptosis, and necrostatins inhibit RIP1 kinase by targeting this region. The study also shows that necrostatins inhibit RIP1 kinase independently of Hsp90, and that necrostatins are specific inhibitors of RIP1 kinase. The findings highlight the importance of RIP1 kinase in necroptosis and suggest that targeting RIP1 kinase could be a promising therapeutic strategy for diseases involving necrotic cell death.The study identifies RIP1 kinase as a specific target of necrostatins, a class of small-molecule inhibitors of necroptosis. Necroptosis is a regulated form of cell death that shares features with unregulated necrosis. Necrostatin-1 (Nec-1) and other necrostatins inhibit RIP1 kinase activity, which is essential for necroptosis. The study shows that necrostatins, including Nec-1, Nec-3, and Nec-5, target RIP1 kinase in the necroptosis pathway, though through different mechanisms. RIP1 kinase is a key upstream kinase involved in necroptosis activation. The study also demonstrates that necrostatins inhibit RIP1 kinase activity in vitro, and this activity correlates with their ability to inhibit necroptotic cell death. The results suggest that necrostatins are first-in-class inhibitors of RIP1 kinase, offering a potential therapeutic approach for diseases involving necrotic tissue injury. The study further identifies that RIP1 autophosphorylation sites, including Ser14/15, Ser20, Ser161, and Ser166, are involved in RIP1 kinase activity. The T-loop of RIP1 is critical for necroptosis, and necrostatins inhibit RIP1 kinase by targeting this region. The study also shows that necrostatins inhibit RIP1 kinase independently of Hsp90, and that necrostatins are specific inhibitors of RIP1 kinase. The findings highlight the importance of RIP1 kinase in necroptosis and suggest that targeting RIP1 kinase could be a promising therapeutic strategy for diseases involving necrotic cell death.