How to prevent comment spam: moderate first, block repeat sources, then handle links

Preventing comment spam calls for a combination of clear rules, manual moderation, blocking repeat sources, and automated safeguards, rather than just handling links in comments. Google’s developer documentation recommends reviewing suspicious interactions, using blocklists, and adding nofollow or ugc attributes to links in untrusted content. But link attributes cannot replace comment management, nor do they mean spam submissions will stop.

First, clearly state which comments are unacceptable

Google’s developer documentation (S1) recommends publishing a specific abuse policy and allowing trusted users to report suspected spam. For comment sections, the rules should tell users what content is unacceptable, rather than simply stating “No spam.”

An answer on Webmasters Stack Exchange (S2) offers a useful criterion: comments or links should be relevant to the page, useful, and welcome there. This is community management advice, not an official rule that applies to every platform. For example, posting a URL under an unrelated article solely to obtain a backlink would not meet this criterion.

Require approval before suspicious comments go public

Manual moderation prevents spam from appearing publicly as soon as it is submitted. Google’s documentation says this can significantly reduce spam on a platform, but it also adds to the day-to-day management workload. Moderation plans must therefore account for available staffing.

• Use the comment system’s moderation features to hold suspicious interactions for manual approval.
• Build user reputations based on registration status and past interactions, rather than judging users solely on a single comment.
• Include reports from trusted users in the moderation process to help identify suspected abuse.

Address repeat sources and automated registrations separately

If spam repeatedly comes from the same sources, blocklists, plugins, or firewalls can help address it. Google’s documentation lists tools such as Akismet, as well as adding identified spam-source IP addresses to a denylist. These measures target repeated abuse; they do not call for every website to block particular regions across the board.

If commenting requires an account, reCAPTCHA or a similar verification tool can also be added to the registration form to help prevent automated bulk account creation. The documentation also recommends monitoring signals such as form completion time, the number of requests from the same IP range, and registration field contents to identify common spam patterns and help build a reputation system.

Link attributes are an additional safeguard, not a comment filter

For links in untrusted content, Google’s documentation recommends adding nofollow or ugc attributes. This addresses the nature of the links and should not be treated as a substitute for moderation or blocking mechanisms.

A Webmasters Stack Exchange discussion (S18) notes that some spam scripts only submit content and do not check how a website handles links. Even if links are removed, the scripts may continue submitting. Therefore, “links have been handled” does not mean “spam comments have been blocked.” Safeguards at the point of submission and moderation before publication are still needed.