Given the various benefits of social media for governments, municipalities are increasingly attempting to institutionalize their use of social media. This article looks at the use of middleware that is observed on municipal Twitter accounts in Dutch municipalities in 2018 and 2021 (N = 724), which provide a set of APIs that specify input and output modalities. It is observed that the use of subscription-based customer relationship management (CRM) tools, developed mostly in a corporate context, has grown considerably, with an uptake of 89.0% of Dutch municipalities in 2021, whereas the use of free CRM tools appears to be declining. Middleware were studied and linked to three models of social media institutionalization (informal experimentation, centralization, and distribution). Municipalities in the informal experimentation model were observed to have smaller population sizes and generally had fewer IT professionals in their constituencies. Larger municipalities with more IT professionals were mostly observed to have a centralized model of institutionalization. Although municipalities with a distributed institutionalization model were larger, they were generally less urbanized. Finally, more technologically advanced municipalities were only observed to make more use of the distributed model.