Foster's role for the 2013 season is unknown at this point, but at the very least, he is an experienced backup who can play guard or tackle.
There's a good shot that Foster will compete for the starting job at left guard. Willie Colon, last year's starter at left guard, could be released. The move would save the Steelers $1.9 million off the cap. There's also the possibility of moving Kelvin Beachum, a seventh-round pick from a year ago, from tackle to guard.
Before bringing back Foster, Pittsburgh was $3.4 million under the cap.
The 27-year-old Foster, a former undrafted rookie in 2009, has been one of the more underappreciated linemen on the Steelers. He has been the team's most durable lineman, starting all 16 games last year (13 at right guard when David DeCastro was hurt and three at left guard when Willie Colon was injured).
ESPN.com AFC North blogger Jamison Hensley contributed to this report.