]> Google LLC

garyillyes@google.com

Ericsson

mirja.kuehlewind@ericsson.com

Blind Five Year Old

aj@blindfiveyearold.com

next generation unicorn sparkling distributed ledger This document describes best practices for web crawlers. Discussion Venues Source for this draft and an issue tracker can be found at .

Introduction Automatic clients, colloquially referred to as crawlers and bots, are used to access web resources, including indexing for search engines or, more recently, training data for new artificial intelligence (AI) applications. As crawling activity increases, automatic clients must behave appropriately and respect the constraints of the resources they access. This includes clearly documenting how they can be identified and how their behavior can be influenced. Therefore, crawler operators are asked to follow the best practices for crawling outlined in this document. For the purposes of this document, a crawler is an automated HTTP client that retrieves resources across one or more web sites without direct human initiation of individual requests. A crawler discovers URIs during retrieval and schedules them for later processing. It relies on algorithmic prioritization and protocol-level instructions such as the Robots Exclusion Protocol to govern its behavior. Note that these best practices are intended for crawlers, and are not necessarily appropriate for all automated clients (all "bots"), particularly user-directed AI agents, but other (non-crawler) bots may choose to adopt similar practices. Furthermore, there are valid reasons why some legitimate crawlers cannot or should not be expected to adopt these practices. For example, while self-declared research crawlers, including privacy and malware discovery crawlers, and contractual crawlers, are welcome to adopt these practices, due to the nature of their relationship with sites, they may choose not to follow all of these practices. Crawler operators that adopt these voluntary practices are encouraged to engage with efforts to develop new standards and practices for bots, and to revisit the recommended best practices as the state of the art evolves.

Recommended Best Practices The following best practices are already applied by a vast majority of large-scale crawlers on the Internet. Crawlers SHOULD:

1. Support and respect the Robots Exclusion Protocol.
2. Be easily identifiable through their user agent string.
3. Not interfere with the regular operation of a site.
4. Support caching directives.
5. Expose the ranges they are crawling from in a standardized format.
6. Expose a page that explains how the crawling can be blocked, whether the page is rendered, and how the crawled data is used.

Support and respect the Robots Exclusion Protocol Crawlers SHOULD support the REP as defined in to allow site owners to opt out from crawling. Especially if the website chooses not to use a robots.txt file as defined by the REP, crawlers further need to respect the X-robots-tag in the HTTP header.

Be easily identifiable through their user agent string As outlined in (Robots Exclusion Protocol; REP), the HTTP request header User-Agent SHOULD clearly identify the crawler, usually by including a URL that hosts the crawler's description. For example: This is already a widely accepted practice among crawler operators. To remain compliant, crawler operators MUST include unique identifiers for their crawlers in the case-insensitive User-Agent header, such as "contains 'googlebot' and 'https://url/...'". Additionally, the name SHOULD clearly identify both the crawler owner and its purpose as much as reasonably possible. Crawler operators that use cryptographic authentication SHOULD use a distinct Signature-Agent URL, and therefore a distinct key directory, for each crawler purpose, as described in . This is the cryptographic counterpart of the purpose identification in the User-Agent header.

Do not interfere with the normal operation of a site Depending on a site's setup (computing resources and software efficiency) and its size, crawling may slow down the site or even take it offline altogether. Crawler operators SHOULD ensure that their crawlers are equipped with back-out logic that relies on at least the standard signals defined by , preferably also additional heuristics such as a change in the relative response time of the server. Therefore, crawlers SHOULD log already visited URLs, the number of requests sent to each resource, and the respective HTTP status codes in the responses, especially if errors occur, to prevent repeatedly crawling the same source. Using the same data, crawlers SHOULD, on a best effort basis, crawl the site at times of the day when the site is estimated to have fewer human visitors. Generally, crawlers SHOULD avoid sending multiple requests to the same resources at the same time and SHOULD limit the crawling speed to prevent server overload, if possible, following the limits outlined in . Additionally, resources SHOULD NOT be re-crawled too often. Ideally, crawlers SHOULD restrict the depth of crawling and the number of requests per resource to prevent loops. Crawlers SHOULD NOT attempt to bypass authentication or other access restrictions, such as when login is required, CAPTCHAs are in use, or content is behind a paywall, unless explicitly agreed upon with the website owner. Crawlers SHOULD primarily access resources using HTTP GET requests, resorting to other methods (e.g., POST, PUT) only if there is a prior agreement with the publisher or if the publisher's content management system automatically makes those calls through client side code (e.g., JavaScript). Generally, the load caused by executing client side code should be carefully considered or even avoided whenever possible.

Support caching directives HTTP caching removes the need of repeated access from crawlers to the same URL.

Expose the IP ranges they use for crawling To complement the , crawler operators SHOULD publish the IP ranges they have allocated for crawling in format, and keep this information reasonably up-to-date, according to the specification. The resource containing the IP addresses SHOULD be linked from the page describing the crawler using the client-ranges relation. To facilitate efficient machine discovery. This relation SHOULD be provided via an HTTP Link header or as a <link> element in the page's HTML metadata section (as defined in ). For example: ]]>

Explain how the crawled data is used and how the crawler can be blocked Crawlers SHOULD be easily identifiable through their user-agent string, and they SHOULD explain how the data they collect will be used. In practice, this is usually done via the documentation page linked in the crawler's user agent. Additionally, the documentation page SHOULD include a contact address for the crawler owner. The documentation SHOULD also provide an example file to block the crawler and a method for verifying files. If the crawler has exempted itself of these best practices, the documentation page SHOULD describe the reason for that. All endpoints hosting identification, documentation, and IP range data must be publicly and highly available, and served with minimal latency for programmatic access.

Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Security Considerations The best practices described in this document, as well as opt-out mechanisms such as and X-robots-tag, are voluntary and do not constitute access control or content security measures. Malicious or non-conformant clients can ignore these practices. To restrict access to sensitive resources, website owners SHOULD employ appropriate security mechanisms at the application or transport layer, such as HTTP Authentication . The User-Agent header field is unauthenticated and trivially spoofed. Website operators MUST NOT rely solely on the User-Agent string to grant privileged access or bypass security controls. When verifying a crawler's identity, website operators SHOULD corroborate the request's source IP address against the crawler operator's published IP ranges or use cryptographic authentication mechanisms where available. Endpoints hosting crawler documentation, client-ranges link relations , and IP range files SHOULD be served over HTTPS using Transport Layer Security (TLS) so that consumers can verify the authenticity and integrity of the published IP ranges before using them in access control or rate-limiting decisions. Even legitimate crawlers can inadvertently degrade website availability or cause a denial of service if they crawl too aggressively, become trapped in infinite URI spaces, or trigger expensive server-side or client-side processing. Implementing the back-out, rate-limiting, and caching practices in this document mitigates, but does not eliminate, this risk. The security considerations of , , , , and also apply.

IANA Considerations This document has no IANA actions.

References Normative References Google LLC. This document extends RFC9309 by specifying additional URL level controls through an HTTP response header and, for historical reasons, through HTML meta tags originally developed in 1996. Additionally it moves the HTTP response header out of the experimental header space (i.e., "X-") and defines the combinability of multiple headers, which was previously not possible. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages. This document obsoletes RFC 7234. This specification defines a model for the relationships between resources on the Web ("links") and the type of those relationships ("link relation types"). It also defines the serialisation of such links in HTTP headers with the Link header field. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230. Cloudflare Google This document describes a protocol for identifying automated traffic using [HTTP-MESSAGE-SIGNATURES]. The goal is to allow automated HTTP clients to cryptographically sign outbound requests, allowing HTTP servers to verify their identity with confidence. It defines the Signature-Agent header field for in-band key discovery, a key directory format based on JWKS, and a well-known URI at which that directory is served. Independent This document defines a standardized JSON format for operators of automated HTTP clients (e.g., web crawlers, AI bots) to publicly disclose their IP address ranges. A consistent, machine-readable format for IP range publication simplifies the task of identifying and verifying legitimate automated traffic, thereby decreasing maintenance load on website operators while reducing the risk of inadvertently blocking beneficial clients. This specification codifies and extends common existing practices to provide a simple yet extensible format that accommodates a variety of use cases. This document specifies and extends the "Robots Exclusion Protocol" method originally defined by Martijn Koster in 1994 for service owners to control how content served by their services may be accessed, if at all, by automatic clients known as crawlers. Specifically, it adds definition language for the protocol, instructions for handling errors, and instructions for caching. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References WHATWG

Acknowledgments TODO acknowledge.