According to social-functionalist accounts of emotion, emotion expressions signal information that guides social interactions. For example, outrage expresses disapproval of an actor’s behavior and can discourage future norm violations. We examined whether this important social function of outrage is maintained in social media environments where communication norms can rapidly update within politically homogenous social networks. Specifically, we tested whether liberals and conservatives perceive outrage expressed towards controversial politicians similarly or differently. Toward this end, we collected a large data set (N = 16,000) of real political tweets authored by ordinary citizens. An equal number of liberal and conservative participants (N = 640) rated the tweets in terms of whether outrage was being expressed by the author. Across various measures of interrater reliability, we found evidence that liberals and conservatives perceive online outrage similarly – agreement on outrage expression remained statistically indistinguishable when liberal and conservatives were mixed together compared to when they were separated by ideology. If anything, the largest differences in agreement among liberals and conservatives appeared when rating liberal outrage. These findings are important for understanding (1) the social functions of emotion in online environments and (2) the role of emotion perception in political polarization unfolding on social media.