Nofollow

Key takeaways

Nofollow belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Nofollow to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Nofollow from memory before moving on to harder problems.

Reference excerpt

Nofollow is a setting on a web page hyperlink that directs search engines not to use the link for page ranking calculations. It is specified in the page as a type of link relation; that is: <a rel="nofollow" ...>. Because search engines often calculate a site's importance according to the number of hyperlinks from other sites, the nofollow setting allows website authors to indicate that the presence of a link is not an endorsement of the target site's importance.

Concept and specification The nofollow value was originally suggested to stop comment spam in blogs. Believing that comment spam affected the entire blogging community, in early 2005 Google's Matt Cutts and Blogger's Jason Shellen proposed the value to address the problem. The specification for nofollow is copyrighted 2005–07 by the authors and subject to a royalty-free patent policy, e.g. per the W3C Patent Policy 20040205, and IETF RFC 3667 and 3668.

Example HTML:

Introduction and support Google announced in early 2005 that hyperlinks with rel="nofollow" would not influence the link target's PageRank. In addition, the Yahoo and Bing search engines also respect this attribute value. On June 15, 2009, Google software engineer Matt Cutts announced on his blog that GoogleBot changed the way it treats nofollowed links, in order to prevent webmasters from using nofollow for PageRank sculpting. Prior to this, webmasters would place nofollow tags on some of their links in order to maximize the PageRank of the other pages. As a result of this change, the usage of nofollow leads to the evaporation of the pagerank of outgoing normal links as they started counting total links while calculating page rank. The new system divides page rank by the total number of outgoing links irrespective of nofollow or follow links, but passes the page rank only through follow or normal links. Cutts explained that if a page has 5 normal links and 5 nofollow outgoing links, the page rank will be divided by 10 links and one share is passed by 5 normal links. However, as of March 1 2020, Google is treating the nofollow link attribute as a hint, rather than a directive, for crawling and indexing purposes.

Interpretation by the individual search engines While all engines that use the nofollow value exclude links that use it from their ranking calculation, the details about the exact interpretation of it vary from search engine to search engine.

Google states that their engine "in general" takes "nofollow" literally and does not "follow" the link. Yahoo! follows it, but excludes it from their ranking calculation. Bing may not follow it, but they exclude it from their ranking calculation. Ask.com also respects the attribute.

Use by websites Many weblog software packages mark reader-submitted links this way by default (often with no option to disable it, except for modification of the software's code). More sophisticated server software could suppress the nofollow for links submitted by trusted users like those registered for a long time, on a whitelist, or with an acceptable karma level. Some server software adds rel="nofollow" to pages that have been recently edited but omits it from stable pages, under the theory that stable pages will have had offending links removed by human editors. The widely used blogging platform WordPress versions 1.5 and above automatically assign the nofollow attribute to all user-submitted links (comment data, commenter URI, etc.). However, there are several free plugins available that automatically remove the nofollow attribute value. Social bookmarking and photo sharing websites that use the rel="nofollow" tag for their outgoing links include YouTube and Digg.com (for most links); websites that don't use the rel="nofollow" tag include Yahoo! My Web 2.0, Technorati Favs, and Propeller.com (no longer an active website).

Repurpose

Control internal PageRank flow Search engine optimization professionals started using the nofollow attribute to control the flow of PageRank within a website, but Google has since corrected this error, and any link with a nofollow attribute decreases the PageRank that the page can pass on. This practice is known as "PageRank sculpting". This differs from the attribute's original intended purpose. nofollow was designed to control the flow of PageRank from one website to another. However, some search engine optimization practitioners have suggested that a nofollow used for an internal link should work just like nofollow used for external links. Several SEOs have suggested that pages such as "About Us", "Terms of Service", "Contact Us", and "Privacy Policy" pages are not important enough to earn PageRank, and so should have nofollow on internal links pointing to them. Google employee Matt Cutts has provided indirect responses on the subject, but has never publicly endorsed this point of view. The practice is controversial and has been challenged by some SEO professionals, including Shari Thurow and Adam Audette. Site search proponents have pointed out that visitors do search for these types of pages, so using nofollow on internal links pointing to them may make it difficult or impossible for visitors to find these pages in site searches powered by major search engines. Although proponents of use of nofollow on internal links have cited an inappropriate attribution to Matt Cutts (see Matt's clarifying comment, rebutting the attributed statement) as support for using the technique, Cutts himself never actually endorsed the idea. Several Google employees (including Matt Cutts) have urged Webmasters not to focus on manipulating internal PageRank. Google employee Adam Lasnik has advised webmasters that there are better ways (e.g. click hierarchy) than nofollow to "sculpt a bit of PageRank", but that it is available and "we're not going to frown upon it". YouTube, a Google company, uses nofollow on a number of internal "help" and "share" links.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Nofollow

Start with the simplest possible case. Write down what Nofollow claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Nofollow before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Nofollow ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Nofollow

In research: Nofollow appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Nofollow in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Nofollow is common in secondary-school and first-year university syllabi. It links to neighbouring topics Microformats, Search engine optimization, Spamming, so understanding it makes those chapters shorter.
In everyday life: Look for Nofollow outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Nofollow in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Nofollow means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Nofollow out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Nofollow in simple terms?

Nofollow is a setting on a web page hyperlink that directs search engines not to use the link for page ranking calculations. It is specified in the page as a type of link relation; that is: <a rel="nofollow" ...>.

Why does Nofollow matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Nofollow?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Nofollow.