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, but, while it looks simple, 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.
- 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
- Robots.txt syntax
- See the code
What is a robots.txt file?
A robots.txt file is a text file which is read by search engine spiders and follows a strict syntax. These spiders are also called robots – hence the name – and the syntax of the file is strict simply because it has to be computer-readable. That means there’s no room for error here – something is either 1, or 0.
Also called the “Robots Exclusion Protocol”, the robots.txt file is the result of a consensus among early search engine spider developers. It’s not an official standard set by any standards organization, but all major search engines adhere to it.
What does the robots.txt file do?
Search engines index the web by spidering pages, following links to go from site A to site B to site C and so on. Before a search engine spiders any page on a domain it hasn’t encountered before, it will open that domain’s robots.txt file, which tells the search engine which URLs on that site it’s allowed to index.
Search engines typically cache the contents of the robots.txt, but will usually refresh it several times a day, so changes will be reflected fairly quickly.
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
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 SEOs call this the crawl budget. This means that if you block sections of your site from the search engine spider, you can allow your crawl budget to be used for other sections.
It can sometimes be highly 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 and sort. Let’s say you have 10 different query parameters, each with different values that can be used in any combination. This leads to hundreds if not thousands of possible URLs. Blocking all 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.
This line blocks all URLs on your site containing a query string:
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.
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):
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
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:
|Bing||Images & Video|
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.
With only one character less, the example below would allow all search engines to crawl your entire site.
The example below would block Google from crawling the
Photo directory on your site – and everything in it.
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
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:
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:
/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
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:
The only other way of achieving the same result without an
allow directive would have been to specifically
disallow every single file in the
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
www.example.com. Simply specifying it like this does the trick:
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
Yahoo!, 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 Yahoo! and Bing to wait 10 seconds after a crawl action, while Yandex would only access your site once in every 10 seconds. It’s a semantic difference, but still interesting to know. Here’s the example
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
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.
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).