Prefer the standard and far more common all right to the colloquial but uncommon alright. Some writers think that alright differs from all right in that the latter means all are correct while the former means all are safe or okay. This mode of thinking likely stems from similar linguistic differences seen in already (before, by now) and all ready (all prepared) or altogether (totally) and all together (all at once, all in one group). However, such distinction does not translate to all right.