Be aware that URLs with and without the "www." prefix can, and probably do, have different PageRank values. For internal pages the "http://" prefix might also matter. Generally speaking, you want to enter URLs for this tool with the "www." prefix, and without the "http://" prefix. (there are exceptions to this advice—for instance, most sub-domains shouldn't have a www. prefix)
Notes on Google ToolBar PageRank:
- The PageRank of a page as displayed according to the Google Toolbar is not necessarily accurate; the actual, current PageRank of a page can be different in Google's databases.
- Toolbar PR is just a snapshot of what the PageRank of a URL was at a certain moment in time.
- Toolbar PageRank values are updated infrequently, and thus can be out of date. Additionally, Google Toolbar PageRank values can be "guesses"—numbers that the toolbar guessed on the spot, based on the parent domain's PageRank. Because of this, a page that is not even indexed by Google can appear to have a PageRank.
- There are also various tricks for "faking" PageRank. For instance, it is possible to fool the Google ToolBar into thinking one site is another site, and thus mimic the other site's PageRank. The Google spider itself will not be fooled, so this fake PageRank has no value.
"Real", Current PageRank?
The "Real" PageRank value in the results table that this tool generates is a possibility for the current real-time PageRank of the page. This is extracted from the Google XML query page for the URL. The XML query page for a URL lists rank information for a series of URLs related to that page, which may or may not include rank information on the URL itself. If it does include the rank for the URL, then that is displayed.
This rank value may represent the real, current PageRank of the page—though what it actually represents is uncertain. It is almost certain it represents a Google PageRank value of some sort; and it seems very probable that this value is more up-to-date and accurate than the corresponding value on the Google Toolbar. Newer sites that should have PR but do not according to the Toolbar, do have PageRank values according to this rank value. Sometimes, this PR value fluctuates on a daily basis; so some sort of updating does appear to be going on here.
It must be emphasized that we cannot be certain how accurate and current this "Real Pagerank?" value is. Some XML pages do not list rank information for the query URL itself. Also, the rank features page gives different results depending on what your geographic location is/what datacenter you are using.
Source code and basic instructions for the PHP PageRank function used here: PageRank script source code