djwebb2021 wrote:
Well, if it says "go rabhadar", it's Munster. If it says "go raibh siad" it's not.
Except where that's used a lot in Conamara.
Really, the quickest way is rule out Conamara/Connacht more generally. In the lines of what was said, look for synthetic forms. If they're present, it's most likely Munster (outside of -im). Then look for tell-tale signs of Donegal Irish, namely the lenition in the dative. Then you're probably left with Connacht.
Ruling out the Caighdeán is tricker, and usually involves spelling.
But, really, it's very difficult unless you know a lot about the dialects, as a lot of modern writing, in particular, is mostly dialect-flavoured Caighdeán, and the trait mentioned for Donegal, at least, is accepted in the Caighdeán too. For Connacht, perhaps the most consistent thing would be to look for sa + urú across all positions.