As is the case with many languages, re- search into code-switching in Modern Irish has, until recently, mainly been focused on the spoken language.This paper reports on the annotation of (English) code-switching in a corpus of 1496 Irish tweets and provides a computational analysis of the nature of code-switching amongst Irish- speaking Twitter users, with a view to providing a basis for future linguistic and socio-linguistic studies.Online user- generated content (UGC) is less restric- tive than traditional written text, allowing for code-switching, and as such, provides a new platform for text-based research in this field of study.Analysis of minority language UGC in partic- ular provides much insight into the evolution of these languages in the digital age.1 Introduction User-generated content (UGC) provides an insight into the use of language in an informal setting in a way that previously was not possible.That is to say that in the pre-internet era (where most pub- lished content was curated and edited), text that was available for analysis was not necessarily re- flective of everyday language use.In some bilin- gual environments, the overwhelming dominance of a majority language can sometimes restrict and discourage the natural use of a minority language.Ad- ditionally, various interesting linguistic phenom- ena occur online that may be frowned upon in more formal settings.The present paper aims to investi- gate one such phenomenon among Irish-speaking users of the micro-blogging platform Twitter.This article is licensed under a Creative Commons 4.0 licence, no derivative works, attribution, CC- BY-ND.c 2019 The authors.