The wiki page about it seems like a decent summary:
Gun laws in WashingtonI’m sure someone will be along shortly to point out how terribly inaccurate it is.
Washington state has preemption (at least for now) so localities can’t have anything more restrictive than state law. A WA state CPL or one from a state with reciprocity and you are good to go.
If you are really brave, OC is legal, too.
Although I would expect that to be inviting a LOT of attention in Seattle.
I would and do just use a lot of discretion in Seattle, Tacoma, etc, period. Concealed mean concealed and all that.
Possession is fine. Just don’t have it loaded in your car if you don’t have a CPL that is recognized here.
Also, keep in mind that as of 7/1/2022, magazines holding more than 10 rounds and not already possessed in state are illegal. So if visiting from out of state after that date and something goes really wrong and you get caught with 11+ round mags, you could be charged with that as well. I keep some 10 round mags for that reason when traveling in CA.