Nearly every performance appraisal evaluates qualities like teamwork, attention to detail, dependability, creativity, leadership -- those skills and attributes are basically a given. Every solid employee possesses those important -- and relatively easy to define -- qualities.

In fact, some employees are even exceptional. (Here's how to tell.)

Yet some employees are even more valuable -- not just exceptional, they're indispensable. They possess attributes that aren't found on performance appraisals but nonetheless make a huge impact on the people around them, and especially on a company's results.

Here are nine ways to know an employee is not just great, but indispensable.

1. They never fail to share (or even give away) the credit.

People we hate to work with tend to be extremely political: they jockey, they maneuver, they plot, and they always try to make themselves look better in the eyes of others -- especially at the expense of other people. (After all, if I look good and you look bad, I'm that much further ahead, right?)

Indispensable people know the best glory is reflected glory. They step back from the spotlight. They let others take the credit for hard work. They let others receive the praise for a job well done..

Most of all, they gain a private sense of fulfillment from seeing others receive public recognition -- because that means everyone wins.

2. They always think before they speak and act.

Ever seen someone throw a chair because he thought his instructions had not been followed? I have. Ever seen someone shred an employee for a mistake it turns out that person didn't make? I have.

Ever seen someone speak or act without thinking -- and forever revised your opinion of her? I have.

Indispensable people react instantly to good news. They react instantly to offer recognition, congratulations, and praise.

But they take a long time to think, reflect, and decide the best way to speak and act when problems arise or when mistakes are made. They know their words and actions will leave a lasting impact, so they do everything possible to get it right.

Even when everything around them seems to be going wrong.

3. They make others feel even smarter than they are.

You know that guy. Maybe he's an employee, a colleague, a vendor. He hears an idea. It's a good idea. It's a great idea.

Now it's his idea.

Do it once and people narrow their eyes. Do it twice and resentment simmers. Do it three times and that's the last time anyone ever shares any ideas with you.

Indispensable people have a knack for doing the opposite: they make their ideas feel like our ideas. When that happens we all work harder. We all work with a greater sense of purpose. We all feel like we're part of something bigger.

And we're all more likely to succeed.

4. They never find something to take personally.

A French dilettante once said, "I am such an egotist that if I were to write about a chair, I'd find some way to write about myself."

You know a guy like that. He sees himself as the center of his own universe, at the center of every story he tells -- and the victim of every unfortunate or negative event.

An employee misses work because he's badly injured? Forget him -- look what a mess that makes of my staffing levels! A supplier has a baby and needs to reschedule an appointment? Forget her -- doesn't she know what that does to my schedule?

To those people, whatever happens to someone else -- regardless of how unfortunate or even tragic -- becomes trivial; what matters most is the effect that has on them.

The only things indispensable people take personally are the things they can do to make life better for other people -- because they feel a personal obligation to improve the lives of the people around them.

5. They always find a silver lining.

You land a major customer... but all you can think about is how hard it will be to fulfill all the new orders. You hire a superstar programmer, but all you can think about is how much you have to pay her. You team up with an awesome partner, but all you can think about is the control you'll lose.

Victories, in business and life, are few and far between. Achieving something awesome (or even just a tiny bit cool) takes time and effort, so reasons to celebrate can be rare.

Indispensable people realize that every huge goal is accomplished one small step at a time and rightly feel every step is cause for celebration. They have a knack for finding the silver lining in every dark cloud because they know there is always a silver lining -- you just have to be willing to look.

And by looking, they spread a sense of optimism and enthusiasm -- something that is often in short supply.

6. They listen way more than they talk.

Interrupting isn't just rude. When you interrupt someone what you're really saying is, "I'm not listening to you so I can understand what you are saying; I'm only listening to find a place to jump in and say what I want say."

Indispensable people listen more than they talk. They focus on what others say. They ask questions not to seem smart but to better understand.

They make us feel wise and respected.

And we love them for it.

7. They never actively seek validation.

Everyone likes praise.

But some people need praise. Some people need constant attention. They need constant validation that they are smart, capable, in charge, successful. In fact, they need to know they are smarter, more capable, and more successful than everyone else.

Indispensable people don't care about external validation. They care about feeling good about themselves. The only validation they seek is what they find in the mirror.

Seeking self-worth inside themselves allows them to spend all their energy encouraging, recognizing, and validating other people -- which makes them awesome to work with.

And also makes them awesome friends.

8. They never talk out of school.

It's hard for any of us to resist learning inside scoop. Finding out the reasons behind someone's decisions, the motivations behind someone's actions, the skinny behind someone's hidden agenda -- much less whether Marcy from shipping is really dating Juan in accounting. Those conversations are hard to resist.

Unfortunately, the people who gossip about other people are also gossiping about us, and suddenly the idea of gossip isn't so much fun.

Indispensable people excuse themselves from gossip, and walk away. They don't worry that they'll lose a gossiper's respect -- they know anyone wiling to gossip doesn't respect other people anyway.

Instead, if they decide to share a secret, they speak openly about their own thoughts and feelings. That way they're not gossiping.

They're just being genuine -- and we all love being around people who are genuine.

9. They never jump on a soapbox.

The higher you rise and the more you accomplish, the more likely you are to think you know everything, and the more likely you are to think you need to tell other people everything you know.

Some people speak with much more finality than foundation. Some people think a position or "status" automatically confers wisdom. And that means other people hear but don't listen.

Indispensable people share their thoughts in a humble and unpretentious way. They already know what they know.

They care about what you know.