Below is the API for the OCaml standard library. It's directly copied over from the OCaml Manual, formatted to the Reason syntax and styled accordingly. The API docs are work-in-progress; we'll be polishing these gradually!
If you're targeting JavaScript, the API docs for BuckleScript includes all of below, plus JS-specific APIs.
module Random: sig .. endval init : int -> unit
val full_init : int array -> unit
Random.init but takes more data as seed.val self_init : unit -> unit
/dev/urandom is available on
   the host machine, it is used to provide a highly random initial
   seed.  Otherwise, a less random seed is computed from system
   parameters (current time, process IDs).val bits : unit -> int
val int : int -> int
Random.int bound returns a random integer between 0 (inclusive)
     and bound (exclusive).  bound must be greater than 0 and less
     than 230.val int32 : Int32.t -> Int32.t
Random.int32 bound returns a random integer between 0 (inclusive)
     and bound (exclusive).  bound must be greater than 0.val nativeint : Nativeint.t -> Nativeint.t
Random.nativeint bound returns a random integer between 0 (inclusive)
     and bound (exclusive).  bound must be greater than 0.val int64 : Int64.t -> Int64.t
Random.int64 bound returns a random integer between 0 (inclusive)
     and bound (exclusive).  bound must be greater than 0.val float : float -> float
Random.float bound returns a random floating-point number
   between 0 and bound (inclusive).  If bound is
   negative, the result is negative or zero.  If bound is 0,
   the result is 0.val bool : unit -> bool
Random.bool () returns true or false with probability 0.5 each.State manipulate the current state
    of the random generator explicitly.
    This allows using one or several deterministic PRNGs,
    even in a multi-threaded program, without interference from
    other parts of the program.module State: sig .. end
val get_state : unit -> State.t
val set_state : State.t -> unit