Citizens often attempt to interact with government through online modes of communication such as email and social media. Using an audit study, we examine when and how American municipalities with populations of over 50,000 respond to online requests for information. We develop baselines for municipal responsiveness, including the average rate, time, and quality of responses, and examine whether these response attributes vary based on the mode of communication or the tone of the request. Overall, municipalities responded to 54% of email requests and 38% of Twitter requests. A majority of responses were received on the same business day. Responses are slightly faster on Twitter, but of higher quality on email. Governments are more likely to respond to frustrated constituents on email, but respond faster to frustrated queries on Twitter, though with lower quality responses. These findings contribute to our understanding of local government responsiveness and have significant implications for democratic accountability and resident compliance with and the effectiveness of local government policies. Furthermore, our scholarly understanding of local government communications with residents, and particularly the promise of social media as a tool of two-way communication, may be underdeveloped.