How much should a tour guide in Ireland be tipped?

One should always tip according to the quality of service. Someone who is entertaining you should be rewarded thusly. If they are making it seem like it is a chore to show you around them piss on them. If they keep you entertained the whole time then 5 to 10 wouldn't be unreasonable. They have bills to pay too you know...

There are no rules on tipping in Ireland, whether in restaurants, bars or anywhere else for that matter. Generally, there is a service charge built in to most costs and though people do appreciate it when they get tips, they are not expected.

It is up to the individual person I would tip about 10 euro

I think 5euro is average from each individual..though nobody will say no to more!