The sandbox effect (or sandboxing) is a theory about the way Google ranks web pages in its index. Its possible existence has been written about since 2004, but not confirmed, with several statements to the contrary.

According to the theory of the sandbox effect, links that may normally be weighted by Google's ranking algorithm but don't improve the position of a webpage in Google's index, could be subjected to filtering to prevent their full impact. Some observations have suggested that two important factors causing this filter are the active age of a domain and the competitiveness of the keywords used in links.

Active age of a domain should not be confused with the date of registration on a domain's WHOIS record, but instead refers to the time when Google first indexed pages on the domain. Keyword competitiveness refers to the search frequency of a word on Google search, with observation suggesting that the higher the search frequency of a word, the more likely the sandbox filter effect will come into play.

While the presence of the Google sandbox has long been debated, Google has made no direct disclosure. However, as the sandbox effect almost certainly refers to a set of filters in play for anti-spam purposes, it is unlikely Google would ever provide details on the matter. However, in one instance, Google's John Mueller did mention that "it can take a bit of time for search engines to catch up with your content, and to learn to treat it appropriately. It's one thing to have a fantastic website. Still, search engines generally need a bit more to be able to confirm that and to rank your site‍—‍your content‍—‍appropriately". This could be understood as the cause for the sandbox effect.

Google has long been aware that its historical use of links as a "vote" for ranking web documents can be subject to manipulation and stated such in its original IPO documentation. Over the years, Google has filed a number of patents that seek to qualify or minimise the impact of such manipulation, which Google terms as "link spam".

Link spam is primarily driven by search engine optimizers, who attempt to manipulate Google's page ranking by creating many inbound links to a new website from other websites they own. Some SEO experts also claim that the sandbox only applies to highly competitive or broad keyword phrases and can be counteracted by targeting narrow or so-called long-tail phrases.

Google has been updating its algorithm for as long as it has been fighting the manipulation of organic search results. However, until May 10, 2012, when Google launched the Google Penguin update, many people wrongly believed low-quality backlinks would not negatively affect a site ranking; Google had been applying such link-based penalties for many years but not made public how the company approached and dealt with what they called "link spam". Since then, there has been a much wider acknowledgment of the dangers of bad SEO and forensic analysis of backlinks to ensure no harmful links. As a result, the algorithm penalised Google's own products too. A well-known example is Google Chrome, which was penalised for purchasing links to boost the web browser's results.

Penalties are generally caused by manipulative backlinks intended to favor particular companies in the search results. By adding such links, companies break Google's terms and conditions. When Google discovers such links, it imposes penalties to discourage other companies from following this practice and to remove any gains that may have been enjoyed from such links. Google also penalizes those who took part in the manipulation and helped other companies by linking to them. These types of companies are often low-quality directories that list a link to a company website with manipulative anchor text for a fee. Google argues that such pages offer no value to the Internet and are often deindexed. Such links are often referred to as paid links.