It is a janya rāgam (derived scale), as it does not have all the seven swaras (musical notes).
It is a pentatonic scale (audava-audava rāgam[1][2] in Carnatic music classification).
Its ārohaṇa-avarohaṇa structure (ascending and descending scale) is as follows (see swaras in Carnatic music for details on below notation and terms): (the notes used in this scale are shadjam, antara gandharam, panchamam, chathusruthi dhaivatham and kaisiki nishadham) Valaji is considered a janya rāgam of Chakravakam, the 16th Melakarta rāgam, though it can be derived from other melakarta rāgams, Harikambhoji, Vagadheeswari, Ramapriya, Vachaspati or Nasikabhooshani, by dropping both rishabham and madhyamam.
Since Chakravakam is lowest in ordinal number among these 6 melakarta scales, Valaji is associated with it.
Valaji's notes when shifted using Graha bhedam, yields another pentatonic rāgam Abhogi.