Both extensions surface search volume data while you browse, saving a trip to a separate keyword research tool. Keyword Surfer works only on Google and stays free, while Keywords Everywhere covers more sites and metrics but runs on a paid credit system instead of being free.
Where each extension shows data
Keyword Surfer adds search volume and related keywords directly on the Google search results page. Keywords Everywhere works more broadly, showing volume and CPC data on Google, YouTube, Amazon and several other sites, which matters if you research keywords beyond Google search.
Pricing: free vs paid credits
Keyword Surfer is free to use with no credits or subscription required, though its data set is more limited. Keywords Everywhere runs on a prepaid credit system: you buy a package of credits and each keyword lookup uses a small amount, so cost scales with how much you search.
Depth of keyword metrics
Keyword Surfer shows core numbers like monthly search volume and a short list of related terms. Keywords Everywhere adds more detail such as CPC, competition score and trend data, which suits people doing regular SEO or PPC research rather than occasional lookups.