How Google interprets the robots.txt specification
Google's automated crawlers support the Robots Exclusion Protocol (REP). This means that before crawling a site, Google's crawlers download and parse the site's robots.txt file to extract information about which parts of the site may be crawled. The REP isn't applicable to Google's crawlers that are controlled by users (for example, feed subscriptions), or crawlers that are used to increase user safety (for example, malware analysis).
What is a robots.txt file
If you don't want crawlers to access sections of your site, you can create a robots.txt file with appropriate rules. A robots.txt file is a simple text file containing rules about which crawlers may access which parts of a site. For example, the robots.txt file for example.com may look like this:
# This robots.txt file controls crawling of URLs under https://example.com. # All crawlers are disallowed to crawl files in the "includes" directory, such # as .css, .js, but Googlebot needs them for rendering, so Googlebot is allowed # to crawl them. User-agent: * Disallow: /includes/ User-agent: Googlebot Allow: /includes/ Sitemap: https://example.com/sitemap.xml
File location and range of validity
You must place the robots.txt file in the top-level directory of a site, on a supported
protocol. In case of Google Search, the supported protocols are HTTP,
HTTPS, and FTP. On HTTP and HTTPS, crawlers fetch the robots.txt file with an HTTP
non-conditional GET request; on FTP, crawlers use a standard
RETR (RETRIEVE) command, using anonymous login.
The rules listed in the robots.txt file apply only to the host, protocol, and port number where the robots.txt file is hosted.
Examples of valid robots.txt URLs
The following table contains examples of robots.txt URLs and what URL paths they're valid for.
| Robots.txt URL examples | |
|---|---|
http://example.com/robots.txt |
Valid for:
|
http://www.example.com/robots.txt |
Valid for:
Not valid for:
|
http://example.com/folder/robots.txt |
Not a valid robots.txt file. Crawlers don't check for robots.txt files in subdirectories. |
http://www.exämple.com/robots.txt |
Valid for:
Not valid for:
|
ftp://example.com/robots.txt |
Valid for:
Not valid for:
|
http://212.96.82.21/robots.txt |
Valid for:
Not valid for:
|
http://example.com:80/robots.txt |
Valid for:
Not valid for:
|
http://example.com:8181/robots.txt |
Valid for:
Not valid for:
|
Handling of errors and HTTP status codes
When requesting a robots.txt file, the HTTP status code of the server's response affects how the robots.txt file will be used by Google's crawlers. The following table summarizes how Googlebot treats robots.txt files for different HTTP status codes.
| Handling of errors and HTTP status codes | |
|---|---|
2xx (successful) |
HTTP status codes that signal success prompt Google's crawlers to process the robots.txt file as provided by the server. |
3xx (redirection) |
Google follows at least five redirect hops as defined by
RFC 1945 and then
stops and treats it as a Google doesn't follow logical redirects in robots.txt files (frames, JavaScript, or meta refresh-type redirects). |
4xx (client errors) |
Google's crawlers treat all |
5xx (server error) |
Because the server couldn't give a definite response to Google's robots.txt request,
Google temporarily interprets server errors as if the site is fully disallowed. Google
will try to crawl the robots.txt file until it obtains a non-server-error HTTP status
code. A
If we are able to determine that a site is incorrectly configured to return
|
| Other errors | A robots.txt file which cannot be fetched due to DNS or networking issues, such as timeouts, invalid responses, reset or interrupted connections, and HTTP chunking errors, is treated as a server error. |
Caching
Google generally caches the contents of robots.txt file for up to 24 hours, but may cache it
longer in situations where refreshing the cached version isn't possible (for example, due to
timeouts or 5xx errors). The cached response may be shared by different crawlers.
Google may increase or decrease the cache lifetime based on
max-age Cache-Control
HTTP headers.
File format
The robots.txt file must be a
UTF-8 encoded plain text
file and the lines must be separated by CR, CR/LF, or
LF.
Google ignores invalid lines in robots.txt files, including the Unicode Byte Order Mark (BOM) at the beginning of the robots.txt file, and use only valid lines. For example, if the content downloaded is HTML instead of robots.txt rules, Google will try to parse the content and extract rules, and ignore everything else.
Similarly, if the character encoding of the robots.txt file isn't UTF-8, Google may ignore characters that are not part of the UTF-8 range, potentially rendering robots.txt rules invalid.
Google currently enforces a robots.txt file size limit of 500 kibibytes (KiB). Content which is after the maximum file size is ignored. You can reduce the size of the robots.txt file by consolidating directives that would result in an oversized robots.txt file. For example, place excluded material in a separate directory.
Syntax
Valid robots.txt lines consists of a field, a colon, and a value. Spaces are optional, but
recommended to improve readability. Space at the beginning and at the end of the line is
ignored. To include comments, precede your comment with the # character. Keep in
mind that everything after the # character will be ignored. The general format is
<field>:<value><#optional-comment>.
Google supports the following fields:
user-agent: identifies which crawler the rules apply to.allow: a URL path that may be crawled.disallow: a URL path that may not be crawled..sitemap: the complete URL of a sitemap.
The allow and disallow fields are also called directives.
These directives are always specified in the form of
directive: [path] where [path] is optional. By default, there are no
restrictions for crawling for the designated crawlers. Crawlers ignore directives without a
[path].
The [path] value, if specified, is relative to the root of the website from where
the robots.txt file was fetched (using the same protocol, port number, host and domain names).
The path value must start with / to designate the root and the value is
case-sensitive. Learn more about
URL matching based on path values.
user-agent
The user-agent line identifies which crawler rules apply to. See
Google's crawlers and user-agent strings
for a comprehensive list of user-agent strings you can use in your robots.txt file.
The value of the user-agent line is case-insensitive.
disallow
The disallow directive specifies paths that must not be accessed by the crawlers
identified by the user-agent line the disallow directive is grouped with.
Crawlers ignore the directive without a path.
The value of the disallow directive is case-sensitive.
Usage:
disallow: [path]
allow
The allow directive specifies paths that may be accessed by the designated
crawlers. When no path is specified, the directive is ignored.
The value of the allow directive is case-sensitive.
Usage:
allow: [path]
sitemap
Google, Bing, and other major search engines support the sitemap field in
robots.txt, as defined by sitemaps.org.
The value of the sitemap field is case-sensitive.
Usage:
sitemap: [absoluteURL]
The [absoluteURL] line points to the location of a sitemap or sitemap index file.
It must be a fully qualified URL, including the protocol and host, and doesn't have to be
URL-encoded. The URL doesn't have to be on the same host as the robots.txt file. You can
specify multiple sitemap fields. The sitemap field isn't tied to any specific
user agent and may be followed by all crawlers, provided it isn't disallowed for crawling.
For example:
user-agent: otherbot disallow: /kale sitemap: https://example.com/sitemap.xml sitemap: https://cdn.example.org/other-sitemap.xml sitemap: https://ja.example.org/テスト-サイトマップ.xml
Grouping of lines and rules
You can group together rules that apply to multiple user agents by repeating
user-agent lines for each crawler.
For example:
user-agent: a disallow: /c user-agent: b disallow: /d user-agent: e user-agent: f disallow: /g user-agent: h
In this example there are four distinct rule groups:
- One group for user agent "a".
- One group for user agent "b".
- One group for both "e" and "f" user agents.
- One group for user agent "h".
For the technical description of a group, see section 2.1 of the REP.
Order of precedence for user agents
Only one group is valid for a particular crawler. Google's crawlers determine the correct
group of rules by finding in the robots.txt file the group with the most specific user agent
that matches the crawler's user agent. Other groups are ignored. All non-matching text is
ignored (for example, both googlebot/1.2 and googlebot* are
equivalent to googlebot). The order of the groups within the robots.txt file is
irrelevant.
If there's more than one specific group declared for a user agent, all the rules from the
groups applicable to the specific user agent are combined internally into a single group. User
agent specific groups and global groups (*) are not combined.
Examples
Matching of user-agent fields
user-agent: googlebot-news (group 1) user-agent: * (group 2) user-agent: googlebot (group 3)
This is how the crawlers would choose the relevant group:
| Group followed per crawler | |
|---|---|
| Googlebot News |
googlebot-news follows group 1, because group 1 is the most specific group.
|
| Googlebot (web) | googlebot follows group 3. |
| Googlebot Images |
googlebot-images follows group 2, because there is no specific
googlebot-images group.
|
| Googlebot News (when crawling images) |
When crawling images, googlebot-news follows group 1.
googlebot-news doesn't crawl the images for Google Images, so it only
follows group 1.
|
| Otherbot (web) | Other Google crawlers follow group 2. |
| Otherbot (news) |
Other Google crawlers that crawl news content, but don't identify as
googlebot-news follow group 2. Even if there is an entry for a related
crawler, it is only valid if it's specifically matching.
|
Grouping of rules
If there are multiple groups in a robots.txt file that are relevant to a specific user agent, Google's crawlers internally merge the groups. For example:
user-agent: googlebot-news disallow: /fish user-agent: * disallow: /carrots user-agent: googlebot-news disallow: /shrimp
The crawlers internally group the rules based on user agent, for example:
user-agent: googlebot-news disallow: /fish disallow: /shrimp user-agent: * disallow: /carrots
Rules other than allow, disallow, and user-agent are
ignored by the robots.txt parser. This means that the following robots.txt snippet is treated
as one group, and thus both user-agent a and b are
affected by the disallow: / rule:
user-agent: a sitemap: https://example.com/sitemap.xml user-agent: b disallow: /
When the crawlers process the robots.txt rules, they ignore the sitemap line.
For example, this is how the crawlers would understand the previous robots.txt snippet:
user-agent: a user-agent: b disallow: /
URL matching based on path values
Google uses the path value in the allow and disallow directives as a
basis to determine whether or not a rule applies to a specific URL on a site. This works by
comparing the rule to the path component of the URL that the crawler is trying to fetch.
Non-7-bit ASCII characters in a path may be included as UTF-8 characters or as percent-escaped
UTF-8 encoded characters per
RFC 3986.
Google, Bing, and other major search engines support a limited form of wildcards for path values. These wildcard characters are:
*designates 0 or more instances of any valid character.$designates the end of the URL.
| Example path matches | |
|---|---|
/ |
Matches the root and any lower level URL. |
/* |
Equivalent to /. The trailing wildcard is ignored. |
/$ |
Matches only the root. Any lower level URL is allowed for crawling. |
/fish |
Matches any path that starts with Matches:
Doesn't match:
|
/fish* |
Equivalent to Matches:
Doesn't match:
|
/fish/ |
Matches anything in the Matches:
Doesn't match:
|
/*.php |
Matches any path that contains Matches:
Doesn't match:
|
/*.php$ |
Matches any path that ends with Matches:
Doesn't match:
|
/fish*.php |
Matches any path that contains Matches:
Doesn't match:
|
Order of precedence for rules
When matching robots.txt rules to URLs, crawlers use the most specific rule based on the length of its path. In case of conflicting rules, including those with wildcards, Google uses the least restrictive rule.
The following examples demonstrate which rule Google's crawlers will apply on a given URL.
| Sample situations | |
|---|---|
http://example.com/page |
allow: /p disallow: /
Applicable rule: |
http://example.com/folder/page |
allow: /folder disallow: /folder
Applicable rule: |
http://example.com/page.htm |
allow: /page disallow: /*.htm
Applicable rule: |
http://example.com/page.php5 |
allow: /page disallow: /*.ph
Applicable rule: |
http://example.com/ |
allow: /$ disallow: /
Applicable rule: |
http://example.com/page.htm |
allow: /$ disallow: /
Applicable rule: |