Let me start off by stating that I realise the Jaffna population has come a long way since the end of the civil war - and are still getting back on their feet. However seeing as this hotel is receiving some ravishing reviews I feel it is in place to be candid.
My girlfriend and I were planning to stay 4 nights at Cosy, but only stayed one. This was mainly due to hygienic and comfort reasons. We were first appointed a room on the bottom floor but these smelled awfully moldy, and were dark and damp. The first floor rooms seemed slightly better: no moldy smell, but it was far from clean. Moreover the bathroom was far below par. Our faucet was loose, we had to mcguiver our own solution with rope to even use it. It was hot and there no place to hang your mosquito nets. A ceiling fan was provided - but conveniently hang in the middle of the room, having little to no effect when in bed. The bed sheets, mattresses, floors and towels were far to dirty for us, we left first thing in the morning.
The food, however, is great so please do support Cosy's restaurant part. Indian bread freshly grilled on a stone oven on the terrace. Service is also good, no complaints on that part.
In short I would not recommend Cosy hotel. But the restaurant is certainly worth a trip.