this is an experimental system for transcribing complex rhythms in plain text that's designed to be as simple as possible. the characters used are: .![:].
beats are represented via . and !, where . is a rest and ! is a note. . starts out as whatever amount is convenient for you. for example, !!.! might be used for a 4/4 bar with beats on the 1st, 2nd, and 4th beats.
beats can be subdivided using brackets. [a:b], where a is some number of .s and b is a rhythm, denotes that the rhythm b will take up a beats. for example, ![..:!!!]! could be a 4/4 bar where the second and third beats are a 2:3 triplet.
as an alternative notation, [a:b:c], where a and b are sequences of .s and c is a rhythm, means that the rhythm c will be played where b beats in c is equivalent to a beats in the outside rhythm.
these can also be used with absolute tempi, written as a BPM marking in base 10, possibly with math applied to it. [120:!!!] means that 3 beats take place in half a second, and [120:.:!!!] means that 3 beats take place at half a second each, etc. (an alternative (and not recommended) variation to keep the spec to 5 characters for "reasons" is to allow writing absolute tempi as a.b or a..b, where a and b are series of !s. the tempo is then interpreted as a/b beats per some unit, this unit being beats per second if . is used and BPM if .. is used; for example, !!..! would be 2 BPS = 120 BPM.)
brackets can also be used without : in them to simply mark off a group of beats.
as an example, the rhythm from Strong One [Masked Man] from Mother 3 can be written (approximately; see below) as [!![.:!!]][..:!..!..!.][!][.:....:[.....:!!!]].
the original Strong One used a similar rhythm, [!![.:!!]][..:!..!..!.][!][.:..:!!!], and Masked Man just messes with the tempo. the 29/16 analysis is pretty close to correct, though. more details can be found here. using absolute tempi for precision, Masked Man can be written as [124:.:[!![.:!!]][132:....:!..!..!.][!][161:..:!!!].