science

Noindex

Noindex is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Noindex rather than just read about it. In short: The noindex value of an HTML robots meta tag requests that automated Internet bots avoid indexing a web page. It is also a value of the HTTP response header X-Robots-Tag.

Key takeaways

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

Reference excerpt

The noindex value of an HTML robots meta tag requests that automated Internet bots avoid indexing a web page. It is also a value of the HTTP response header X-Robots-Tag. Reasons why one might want to use this meta tag include advising robots not to index a very large database, web pages that are very transitory, web pages that are under development, web pages that one wishes to keep slightly more private, or the printer and mobile-friendly versions of pages. Since the burden of honoring a website's noindex tag lies with the author of the search robot, sometimes these tags are ignored. Also the interpretation of the noindex tag is sometimes slightly different from one search engine company to the next.

Noindexing entire pages Possible values for the meta tag content are: "none", "all", "index", "noindex", "nofollow", and "follow". A combination of the values is also possible, for example:

Bot-specific directives The noindex directive can be restricted only to certain bots by specifying a different "name" value in the meta tag. For example, to specifically block Google's bot, specify:

Or, to block Bing's bot, specify: Or, to block Baidu's bot, specify:

robots.txt file A robots.txt file can be used to block crawling.

Noindexing part of a page It is also possible to exclude part of a Web page, for example navigation text, from being indexed rather than the whole page. There are various techniques for doing this; it is possible to use several in combination. Google's main indexing spider, Googlebot, is not known to recognize any of these techniques.

<noindex> tag The Russian search engine Yandex introduced a new <noindex>...</noindex> tag which prevents indexing of the content between the tags. To allow the source code to validate,  alternatively can be used: Other indexing spiders also recognize the <noindex>...</noindex> tag, including Atomz.

microformat There is a 2005 draft microformats specification with the same functionality. The Robot Exclusion Profile looks for the attribute and value class="robots-noindex" in HTML tags: A combination of values is also possible, for example:

Yahoo! In 2007, Yahoo! introduced similar functionality to the microformat into its spider. However, Yahoo!'s spider is incompatible in that it looks for the value class="robots-nocontent" and only this value:

SharePoint SharePoint 2010’s iFilter excludes content inside of a <div class="noindex">...</div> tag. Inner s were initially not excluded, but this may have changed. It is also unknown whether the attribute can be applied to tags other than <div>...</div>.

Structured comments

Google Search Appliance The Google Search Appliance uses structured comments: Other indexing spiders also use their own structured comments.

See also Nofollow link attribute Robots Exclusion Standard

References

Worked examples

Example 1 — a first encounter with Noindex

Start with the simplest possible case. Write down what Noindex 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 Noindex 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 Noindex 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 Noindex

In research: Noindex 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 Noindex 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: Noindex is common in secondary-school and first-year university syllabi. It links to neighbouring topics Search engine optimization, World Wide Web, so understanding it makes those chapters shorter.
In everyday life: Look for Noindex 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.

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How to study Noindex in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Noindex 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 Noindex out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Noindex in simple terms?

The noindex value of an HTML robots meta tag requests that automated Internet bots avoid indexing a web page. It is also a value of the HTTP response header X-Robots-Tag.

Why does Noindex 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 Noindex?

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 Noindex.