This study explores whether chat users are able to extend prior, apparently completed posts in the dyadic online text chat context. Dyadic text chat has a unique turn-taking system, and most chat softwares do not permit users to monitor one another's written messages-in-progress. This is likely to impact on their use of online extensions as an interactional resource. For example, intonation is one interactional device used in spoken conversation to indicate imminent turn closure and project a response from interlocutors, thus creating a possibly complete turn-constructional unit (TCU) and transition relevance places (TRP). The speaker, however, may add further talk to that TCU, thus producing an extension and redoing the TRP. If prosody and monitorability of recipients' online talk production are unavailable as interactional resources, can participants still extend prior posts during online textual interaction? The analysis of chat logs of geographically dispersed speakers of Italian provides new evidence on the fundamental role of semantics, pragmatics, syntax, and punctuation in users' deployment of extending devices with various forms and interactional functions in dyadic textual online chat, as resources for social action.