Link exchange is an agreement between two websites to link to each other. It is not forbidden in itself and is common in the business world – a link to a supplier, partner, subsidiary, or joint project is natural and useful. The problem arises with systematic, large-scale exchange whose sole purpose is to manipulate rankings: partner lists with dozens of unrelated sites, three-way exchanges masking reciprocity, and mass outreach offering a mutual link. Search engines recognise such patterns, and the links stop counting, or in a worse case, the site gets penalised. The practical rule is: if a link would make sense even without something given in return, and it helps the reader, it is fine. If it only exists because of an exchange, it probably has no value.
See also: PBN and risky practices, Backlink profile, Guest post.
