CODECS, an acronym for Collaborative Online Database and e-Resources for Celtic Studies, is an online platform published by the A. G. van Hamel Foundation for Celtic Studies, which is based in the Netherlands. It presents an ongoing attempt at building a comprehensive descriptive catalogue of sources of interest to Celtic studies, including every text and manuscript ever written, together with a bibliography which currently holds over 20,000 publications. In addition, to enrich ways in which users can discover and explore these resources of the past, it provides structured information about the contents as well as contexts or provenances of the sources described. This includes making semantic links to persons, places, topics and other entities, which allows for different points of entry to users navigating the site. The focus is on pre-modern sources and current coverage is ‘biased’ towards Irish and Hiberno-Latin material. The software used for data storage and querying is Semantic MediaWiki, which was found to be robust, flexible and pluggable. CODECS plays host to complementary projects such as Tionscadal na Nod, a resource for getting to grips with scribal abbreviations in Irish manuscripts. The website is designed to be collaborative and open to scholars looking to set up new projects within its infrastructure and ecosystem.