Q:

Count vs. mass — where can you look this up?

Most dictionaries don't say whether a noun is count vs. mass.  Short of asking a fluent English speaker, where can you get this kind of information?
I've tried asking various other ESL/EFL people I know this same question, and also tried googling it, but to no avail.

A:

Beware broad-brush approaches, even if you find a dictionary offering the count - uncount classification. Some - perhaps many - nouns are non-count in some senses and count in others. Coffee is a good example - its basic sense is uncount:

Coffee is a drink made by infusing the ground beans of Coffea arabica
  etc.
Too much coffee can be bad for you.

However, different products will be count:

Coffees produced using a higher proportion of robusta beans in the
  blend tend to be bitter and have less flavour but better body than
  those with a higher proportion of arabica beans.

And ellipsis produces another count-noun polyseme:

Two coffees, please.
(ie two cups / mugs of coffee)

Rice is count when different strains are meant, and sand when different sorts are being mentioned. (There is a poetic use of sands also.) Even furnitures is allowed in certain situations.
There are also grey areas - you'd probably ask for less peas rather than fewer peas (especially if they were mushy) on your plate. Non-count doesn't always mean that counting would be impossible - confetti is treated as a singular non-count noun. The difficulty ensuing when one tries to use algae in both count and non-count senses has recently been addressed in a different thread.
A good place to start looking is http://learnenglish.britishcouncil.org/en/english-grammar/nouns/common-problems-countuncount-nouns .

A:

Most English dictionaries used and published in the United States don't include that information, just as they don't provide IPA-based phonemic transcription. However, dictionaries published in the UK and elsewhere sometimes do, especially dictionaries for English learners.
One American online exception is Merriam-Webster's Learner's Dictionary, which dutifully reports that pea and bean are both [count], while rice and sand are both [noncount].

A:

You should try Wiktionary. It lists the plural, or indicates that the noun is uncountable. For example, rice is listed as uncountable, and bean has the plural listed as beans.

