I would say a Coverity installation at Facebook is probably a "let's talk" level of expensive.

That said, paying a team of expert engineers is also very expensive, not to mention the opportunity cost.

Right, and for Facebook internally, whatever the number is, it's a speed bump.

But some reasons not to use Coverity then:

* Doing it in-house gives Facebook near total control over what the system is going to focus on; they can tailor it exactly to their problem set.

* It's a worthwhile open source project, since most values of "expensive" mean "other projects won't ever use it".

* If it gets any traction as an open source project, they can draft off the work other people will put into it.

I'd add

* Facebook has recently hired a number of expert language theorists and practitioners. Doing it in-house

  1) Gives them something to do

  2) Serves to cement Facebook's language-expertise-brand recognition and dominance.

The very fact that hiring is focusing on this group signals to me that this is an area which Facebook takes seriously and wants to be taken seriously in.

If Facebook ever goes down as a social network, they will without doubt still be a powerful technology company.

FB has achieved a vertical integration in the IT world rivaled only by Google, Apple and maybe MS.

It is free for open source projects, but yes expensive otherwise.