Google's Disavow Tool, accessible inside Search Console, allows you to upload a text file telling Google to ignore specific links pointing to your site for ranking purposes. Format: a plain .txt file with one entry per line (`domain:spammydomain.com` to disavow all links from that domain, or full URL to disavow a specific link). When to use it (rare in 2026): (1) You have received a Manual Action penalty for unnatural inbound links and need to disavow before submitting a reconsideration request; (2) You have evidence of a coordinated negative SEO attack (sudden appearance of thousands of new spammy backlinks, often coinciding with ranking drops); (3) You have inherited a site from a previous owner who actively bought spammy links and Google's algorithm is not adequately discounting them. When NOT to use it: (1) Routine clean-up of low-quality links — Google generally ignores these algorithmically and disavowing them adds no benefit; (2) Speculative pre-emption of links you do not like the look of; (3) Trying to recover from algorithmic ranking drops without clear evidence the cause is link-related (most ranking drops in 2026 are content-quality or technical, not link-based). When in doubt, do nothing — disavowing legitimate links is more dangerous than leaving low-quality ones alone.