How Page Rank Tools Calculate PR?

Google doesn't provide it via APIs?

[webgaya]

Hi,

There are plenty of online tools that provides Google Page Rank for given site(s). How do they calculate it? Some even refer to different data centers and future Page Ranks.

As I know Google doesn't provide it via its APIs. Are there any other legal ways to calculate it?

Please provide any tip you know.

Thanks.

[mertero]

I'm also interested in this.

Maybe we should check how it's done in the toolbar, and reverse-engineer it.