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).

This page describes Google's interpretation of the REP. For the original standard, check RFC 9309 .

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 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 Google 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

If you're new to robots.txt, start with our intro to robots.txt . You can also find tips for creating a robots.txt file .

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. The URL for the robots.txt file is (like other URLs) case-sensitive. 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.

Avoid serving different versions of your robots.txt file to different requestors (in other words, cloaking ), as this creates a maintenance burden, may prevent you from debugging crawl issues, or have otherwise unintended consequences.

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. Column one contains the URL of a robots.txt file, and column two contains domains that that robots.txt file would and wouldn't apply to.

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.

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 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 rules 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 (other fields such as crawl-delay aren't supported):

• 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 rules (also known as directives). These rules are always specified in the form of rule: [path] where [path] is optional. By default, there are no restrictions for crawling for the designated crawlers. Crawlers ignore rules 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 rule specifies paths that must not be accessed by the crawlers identified by the user-agent line the disallow rule is grouped with. Crawlers ignore the rule without a path.

Google can't index the content of pages which are disallowed for crawling, but it may still index the URL and show it in search results without a snippet. Learn how to block indexing .

The value of the disallow rule is case-sensitive.

Usage:

disallow: [path]

allow

The allow rule specifies paths that may be accessed by the designated crawlers. When no path is specified, the rule is ignored.

The value of the allow rule 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:

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 rules 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.

The following table shows how the different wildcard characters affect parsing:

Order of precedence for rules

When matching robots.txt rules to URLs, crawlers use the most specific rule based on the length of the rule 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.

allow: /p
disallow: /

allow: /folder
disallow: /folder

allow: /page
disallow: /*.htm

allow: /page
disallow: /*.ph

allow: /$
disallow: /

allow: /$
disallow: /