Virtually every SEO tool is powered by crawled search results. In order to gain more insights from each crawl and thereby reduce costs for the end user, tools often use this parameter to force the display of expanded search results on the homepage instead of the usual 10 regular organic results that users see by default. For example, Moz Pro has long had a standard of &num=50, which is 5 “pages” of results per crawl.
This parameter has actually been deprecated for many years, but is still unofficially supported. In mid-September, it slowly started to stop working, forcing SEO tools to find alternatives. Some tools (including Moz and STAT) prepare an alternative we call “splicing”, where we piece together a series of paged results (10 at a time) into a longer set of results. There are various difficulties associated with this approach, many of which can be mitigated or avoided, but the main impact is on costs, which ultimately increase significantly, in many cases to unsustainable levels.
This should also be seen against the backdrop of a general increase in SERP data costs in recent years, as tools are forced to increasingly mimic real browsers in order to obtain accurate, representative rankings.
