The robots.txt file is one of the main ways of telling a search engine where it can and can’t go on your website. All major search engines support the basic functionality it offers, but some of them respond to some extra rules which can be useful too. This guide covers all the ways to use robots.txt on your website.
Warning!
Any mistakes you make in your robots.txt can seriously harm your site, so make sure you read and understand the whole of this article before you dive in.
Table of contents
- What is a robots.txt file?
- What does the robots.txt file do?
- Where should I put my robots.txt file?
- Pros and cons of using robots.txt
- Pro: managing crawl budget
- Con: not removing a page from search results
- Con: not spreading link value
- Robots.txt syntax
- The user-agent directive
- The most common user agents for search engine spiders
- The disallow directive
- How to use wildcards/regular expressions
- Non-standard robots.txt crawl directives
- The allow directive
- The host directive
- The crawl-delay directive
- The sitemap directive for XML Sitemaps
- The user-agent directive
- See the code
What is a robots.txt file?
A robots.txt file is a text file which is read by search engine (and other systems). Also called the “Robots Exclusion Protocol”, the robots.txt file is the result of a consensus among early search engine developers. It’s not an official standard set by any standards organization; although all major search engines adhere to it.
What does the robots.txt file do?
Search engines discover and index the web by crawling pages. As they crawl, they discover and follow links. This takes them from site A to site B to site C, and so on. But before a search engine visits any page on a domain it hasn’t encountered before, it will open that domain’s robots.txt file. That lets them know which URLs on that site they’re allowed to visit (and which ones they’re not).
Where should I put my robots.txt file?
The robots.txt file should always be at the root of your domain. So if your domain is www.example.com, it should be found at https://www.example.com/robots.txt.
It’s also very important that your robots.txt file is actually called robots.txt. The name is case sensitive, so get that right or it just won’t work.
Pros and cons of using robots.txt
Pro: managing crawl budget
It’s generally understood that a search spider arrives at a website with a pre-determined “allowance” for how many pages it will crawl (or, how much resource/time it’ll spend, based on a site’s authority/size/reputation, and how efficiently the server responds). SEOs call this the crawl budget.
If you think that your website has problems with crawl budget, then blocking search engines from ‘wasting’ energy in unimportant parts of your site might mean that they focus instead on the sections which do matter.
It can sometimes be beneficial to block the search engines from crawling problematic sections of your site, especially on sites where a lot of SEO clean-up has to be done. Once you’ve tidied things up, you can let them back in.
A note on blocking query parameters
One situation where crawl budget is particularly important is when your site uses a lot of query string parameters to filter or sort lists. Let’s say you have 10 different query parameters, each with different values that can be used in any combination (like t-shirts in multiple colors and sizes). This leads to lots of possible valid URLs, all of which might get crawled. Blocking query parameters from being crawled will help make sure the search engine only spiders your site’s main URLs and won’t go into the enormous trap that you’d otherwise create.
Con: not removing a page from search results
Even though you can use the robots.txt file to tell a spider where it can’t go on your site, you can’t use it tell a search engine which URLs not to show in the search results – in other words, blocking it won’t stop it from being indexed. If the search engine finds enough links to that URL, it will include it, it will just not know what’s on that page. So your result will look like this:
If you want to reliably block a page from showing up in the search results, you need to use a meta robots noindex tag. That means that, in order to find the noindex tag, the search engine has to be able to access that page, so don’t block it with robots.txt.
Con: not spreading link value
If a search engine can’t crawl a page, it can’t spread the link value across the links on that page. When a page is blocked with robots.txt, it’s a dead-end. Any link value which might have flowed to (and through) that page is lost.
Robots.txt syntax
A robots.txt file consists of one or more blocks of directives, each starting with a user-agent line. The “user-agent” is the name of the specific spider it addresses. You can either have one block for all search engines, using a wildcard for the user-agent, or specific blocks for specific search engines. A search engine spider will always pick the block that best matches its name.
These blocks look like this (don’t be scared, we’ll explain below):
User-agent: *
Disallow: /
User-agent: Googlebot
Disallow:
User-agent: bingbot
Disallow: /not-for-bing/
Directives like Allow and Disallow should not be case sensitive, so it’s up to you whether you write them lowercase or capitalize them. The values are case sensitive however, /photo/ is not the same as /Photo/. We like to capitalize directives because it makes the file easier (for humans) to read.
The user-agent directive
The first bit of every block of directives is the user-agent, which identifies a specific spider. The user-agent field is matched against that specific spider’s (usually longer) user-agent, so for instance the most common spider from Google has the following user-agent:
Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)
So if you want to tell this spider what to do, a relatively simple User-agent: Googlebot line will do the trick.
Most search engines have multiple spiders. They will use a specific spider for their normal index, for their ad programs, for images, for videos, etc.
Search engines will always choose the most specific block of directives they can find. Say you have 3 sets of directives: one for *, one for Googlebot and one for Googlebot-News. If a bot comes by whose user-agent is Googlebot-Video, it would follow the Googlebot restrictions. A bot with the user-agent Googlebot-News would use the more specific Googlebot-News directives.
The most common user agents for search engine spiders
Here’s a list of the user-agents you can use in your robots.txt file to match the most commonly used search engines:
| Search engine | Field | User-agent |
|---|---|---|
| Baidu | General | baiduspider |
| Baidu | Images | baiduspider-image |
| Baidu | Mobile | baiduspider-mobile |
| Baidu | News | baiduspider-news |
| Baidu | Video | baiduspider-video |
| Bing | General | bingbot |
| Bing | General | msnbot |
| Bing | Images & Video | msnbot-media |
| Bing | Ads | adidxbot |
| General | Googlebot |
|
| Images | Googlebot-Image |
|
| Mobile | Googlebot-Mobile |
|
| News | Googlebot-News |
|
| Video | Googlebot-Video |
|
| AdSense | Mediapartners-Google |
|
| AdWords | AdsBot-Google |
|
| Yahoo! | General | slurp |
| Yandex | General | yandex |
The disallow directive
The second line in any block of directives is the Disallow line. You can have one or more of these lines, specifying which parts of the site the specified spider can’t access. An empty Disallow line means you’re not disallowing anything, so basically it means that a spider can access all sections of your site.
The example below would block all search engines that “listen” to robots.txt from crawling your site.
User-agent: *
Disallow: /
With only one character less, the example below would allow all search engines to crawl your entire site.
User-agent: *
Disallow:
The example below would block Google from crawling the Photo directory on your site – and everything in it.
User-agent: googlebot
Disallow: /Photo
This means all the subdirectories of the /Photo directory would also not be spidered. It would not block Google from crawling the /photo directory, as these lines are case sensitive.
This would also block Google from accessing URLs containing /Photo, such as /Photography/.
How to use wildcards/regular expressions
“Officially”, the robots.txt standard doesn’t support regular expressions or wildcards, however, all major search engines do understand it. This means you can use lines like this to block groups of files:
Disallow: /*.php
Disallow: /copyrighted-images/*.jpg
In the example above, * is expanded to whatever filename it matches. Note that the rest of the line is still case sensitive, so the second line above will not block a file called /copyrighted-images/example.JPG from being crawled.
Some search engines, like Google, allow for more complicated regular expressions, but be aware that some search engines might not understand this logic. The most useful feature this adds is the $, which indicates the end of a URL. In the following example you can see what this does:
Disallow: /*.php$
This means /index.php can’t be indexed, but /index.php?p=1 could be. Of course, this is only useful in very specific circumstances and also pretty dangerous: it’s easy to unblock things you didn’t actually want to unblock.
Non-standard robots.txt crawl directives
As well as the Disallow and User-agent directives there are a couple of other crawl directives you can use. These directives are not supported by all search engine crawlers so make sure you’re aware of their limitations.
The allow directive
While not in the original “specification”, there was talk very early on of an allow directive. Most search engines seem to understand it, and it allows for simple, and very readable directives like this:
Disallow: /wp-admin/
Allow: /wp-admin/admin-ajax.php
The only other way of achieving the same result without an allow directive would have been to specifically disallow every single file in the wp-admin folder.
The host directive
Supported by Yandex (and not by Google, despite what some posts say), this directive lets you decide whether you want the search engine to show example.com or www.example.com. Simply specifying it like this does the trick:
host: example.com
But because only Yandex supports the host directive, we wouldn’t advise you to rely on it, especially as it doesn’t allow you to define a scheme (http or https) either. A better solution that
works for all search engines would be to 301 redirect the hostnames that you don’t want in the index to the version that you do want. In our case, we redirect www.yoast.com to yoast.com.
The crawl-delay directive
Bing and Yandex can sometimes be fairly crawl-hungry, but luckily they all respond to the crawl-delay directive, which slows them down. And while these search engines have slightly different ways of reading the directive, the end result is basically the same.
A line like the one below would instruct those search engines to change how frequently they’ll request pages on your site.
crawl-delay: 10
Do take care when using the crawl-delay directive. By setting a crawl delay of 10 seconds you’re only allowing these search engines to access 8,640 pages a day. This might seem plenty for a small site, but on large sites it isn’t very many. On the other hand, if you get next to no traffic from these search engines, it’s a good way to save some bandwidth.
The sitemap directive for XML Sitemaps
Using the sitemap directive you can tell search engines – specifically Bing, Yandex and Google – where to find your XML sitemap. You can, of course, also submit your XML sitemaps to each search engine using their respective webmaster tools solutions, and we strongly recommend you do, because search engine webmaster tools programs will give you lots of valuable information about your site. If you don’t want to do that, adding a sitemap line to your robots.txt is a good quick alternative.
Sitemap: https://www.example.com/my-sitemap.xml
Validate your robots.txt
There are various tools out there that can help you validate your robots.txt, but when it comes to validating crawl directives, we always prefer to go to the source. Google has a robots.txt testing tool in its Google Search Console (under the ‘Old version’ menu) and we’d highly recommend using that:
Be sure to test your changes thoroughly before you put them live! You wouldn’t be the first to accidentally use robots.txt to block your entire site, and to slip into search engine oblivion!
See the code
In July 2019, Google announced that they were making their robots.txt parser open source. That means that, if you really want to get into the nuts and bolts, you can go and see how their code works (and, even use it yourself, or propose modifications to it).
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