SANTA CLARA, Calif. -- After spending most of his life around NFL franchises, San Francisco 49ers coach Kyle Shanahan has a firm grasp on all that goes into free agency.

The first principle? If you're signing a player, particularly in the first wave of free agency, you're almost certainly overpaying for him. That's because, without exception, the demand always exceeds the supply when it comes to good players hitting the market.

Shanahan has been around long enough to see plenty of signings that have worked and more that haven't. Along the way, he has noted every boom and every bust as well as the positive or negative effects those hits and misses can have on a locker room. To wit, he was the offensive coordinator in Washington for the final year of the Albert Haynesworth debacle.

Which is why, when Shanahan and general manager John Lynch begin their preparation for free agency, they put a premium on two things: talent (of course) and the increasingly pervasive assessment criterion of football character. The former can easily be identified by watching the tape. The latter is a bit more difficult to discern, though it's critically important when it comes to building culture. After all, as Shanahan has been quick to note, players always notice which teammates are getting the biggest paychecks and just how committed to football those players are.

“I think that’s extremely important, especially when it comes to free agency," Shanahan said. "If you bring in the wrong type of guys in free agency, I think it’s one of the most underrated things in how much that can hurt your team. You want to bring in the best players possible, but they have to be the right type of person. It usually starts with the tape. Very rarely, when you watch how guys play, how do they play when they’re down? How do they play from play one to the last play? What type of effort do they give? Is it always as hard as they can go? When you have guys who work their tail off on every play, whether they’re on the backside or the front side, they play physical. They never turn anything down. That usually looks like you’re dealing with the right type of guy."

Having football character at the core of their approach to free agency was simple enough in the Niners' first year with Shanahan and Lynch at the helm. Because they were starting what looked to be a lengthy rebuilding process, they leaned on Shanahan and his coaching staff's experience in the league to add players with whom they'd already built relationships. That meant signing players who could set the right tone, such as receivers Pierre Garcon and Aldrick Robinson, linebacker Malcolm Smith, running back Tim Hightower and quarterback Brian Hoyer.

For as important as their playing ability was, the 2017 free-agent class was just as much about building the type of locker room Shanahan and Lynch envisioned. Others, such as fullback Kyle Juszczyk and receiver Marquise Goodwin, came with sterling reputations for their work ethic in their previous stops.

This year, Lynch and Shanahan didn't view free agency as a place to do a complete makeover. Rather, they wanted to identify a few players at positions of need who not only would make the 49ers better but also fit in to what they started to build in 2017. Absent a market full of obvious fits from previous stops, Shanahan, Lynch and their respective staffs spent the weeks leading up to the start of the new league year doing research on players they believed had the talent to be worth the investments.

They quickly identified center Weston Richburg and running back Jerick McKinnon as their top two priorities based on their talent and ability to fit Shanahan's offense. From there, Shanahan began looking at the little things that determine whether they would fit with the 49ers.

"What goes into that? Well, a lot of things go into it," Lynch said. "We talk a lot about talent and spirit. The talent, we think these guys are tremendous fits for what we do, for what Kyle does in his offense. We think these guys fit just perfectly. We’re excited to use them. And then the spirit. These are guys that we want to build our locker room around. These are stand-up guys, and we’re very pleased to have them as 49ers."

Using McKinnon as an example, Shanahan was impressed with how he played without the ball in his hands. Despite his relatively slight 5-foot-9, 205-pound frame, McKinnon's tape showed a player with full knowledge of the route tree, an indication he put in the work to learn beyond the scope of simply playing running back. When left in to pass protect, Shanahan saw McKinnon unafraid to take on players who were inevitably bigger than he was. He was also impressed by McKinnon's 32 repetitions with 225 pounds on the bench press, a record for running backs at the NFL scouting combine, for it was an indication of McKinnon's commitment in the weight room.

From there, Shanahan, Lynch and their staffs began calling people around the league to find out more. Those conversations aren't limited to league contacts, either. It often means going back to the player's college days and beyond. In McKinnon's case, it meant a conversation with current Niners running back Matt Breida, who was a freshman at Georgia Southern when McKinnon was a senior. Shanahan spent last year around Breida, who at the time was an undrafted rookie trying to make the team. He sees similarities in Breida and McKinnon, with both coming from a smaller school and having the constant motivation that comes from facing questions about their ability to play at the NFL level.

Shanahan and Lynch took a similar approach with Richburg and came to the same conclusion that, even though they hadn't had a chance to work with either player, there was ample evidence to believe strongly enough in both players to sign them to lucrative contracts. The same was true of cornerback Richard Sherman, who has never left any doubt about his love for the game and competitive desire.

"You’ve got to do your homework, and hopefully you have some people who have been around them that you can trust and you try to talk to those people and get an idea," Shanahan said. "I always feel that’s the biggest risk in free agency. We can see what you’re getting on tape, but you don’t know what you’re getting until you go through some adversity with a guy. That’s always the gamble. It’s always easier when you know a guy, too. We’ve looked into how they play on tape. I feel extremely confident that we got the right type of people.”