One of these spellings is common, but wrong.
What’s the Trouble? Nearly all usage guides condemn "alright" (written as one word), but it occasionally shows up in the work of respected writers and many average people think it's fine, or even the preferred spelling.
The Oxford English Dictionary calls "alright" a “frequent spelling of all right”—not quite saying outright that it is wrong, but making the implication. The Columbia Guide to Standard American English is more clear: “All right is the only spelling Standard English recognizes.”
The word’s history is little help. According to the Merriam-Webster Dictionary of English Usage, very early spellings included both one-word and two-word forms such as "ealriht" and "al rizt."
With the pressure to save space in status updates and text messages, "alright" is likely to gain currency rather than fade. The “saves space” argument is not new; an early proponent of "alright" over "all right" mentioned the extra cost of sending cable messages because of the extra characters in "all right."
Until popular usage guides such as the Chicago Manual of Style or AP Stylebook give their stamp of approval to "alright," the word will be edited out of most professional work. However, one telling sign is that many quotations on GoodReads.com, transcribed by people who are likely above-average readers, substitute "alright" when "all right" appears in the original book. I predict "alright" will eventually win.
What Should You Do? Stick with "all right" unless you wish to be part of the charge to legitimize "alright."
Is Bill alright?...Cowley thinks I’m a Simple Simon. I’m a fool alright.
—Jack Kerouac (Beat Generation author of On the Road) in a personal letter to Allen Ginsberg, Peter Orlovsky, William S. Burroughs, and Alan Ansen