underscore-cli is utterly brilliant for this, even better — dare I say it? — than traditional log files with cut/grep/awk. Being able to treat logs as a dataset that can be mapped/reduced/flattened/grouped/otherwise analysed is life-changingly good.

About the strongest endorsement I can give is that it makes me wish more of my logs were in JSON format, rather than wishing that less were as I always had before.