Carswell was placed on the Oakland Raiders practice squad in September of last season after not making the 53-man roster out of training camp. He was released September 12.
The University of Southern California alum graduated from Milpitas High school and went on to play in 40 games for the Trojans. He averaged 9.7 yards per catch in his four collegiate seasons. He made 40 catches in his career and had a high of 18 as a senior.
Carswell will be added to the mix at wide receiver where the club is looking to replace Michael Crabtree, who will be out for a majority of the season after suffering a torn Achilles early on in OTAs.
With Crabtree's absence, former first-round pick A.J. Jenkins, rookie Quinton Patton, Riccardo Lockette, Marlon Moore, Kassim Osgood are battling for roles on the offense. Incumbents Mario Manningham and Kyle Williams are still recovering from knee injuries that ended their 2012 seasons early. Both are slated to be back in time for training camp.