Can I tag my corpus with my own tags?

Yes, this is possible.
By default, Sketch Engine tags and lemmatizes with the built-in tagger. To use your own tagset, the text must be tagged externally and uploaded as a vertical file. Custom tags may not be compatible with the word sketch and thesaurus which make use of the default tagset. For the word sketch to work, the word sketch grammar should be adapted to the new tagset to make them compatible with the custom tagset.

related topics: