Network Working Group                                          G. IllyesInternet-Draft                                               IndependentIntended status: Informational                             M. KuehlewindExpires: 10 April 2026                                          Ericsson                                                                 A. Kohn                                                     Blind Five Year Old                                                          7 October 2025                         Crawler best practices                      draft-illyes-aipref-cbcp-02Abstract   This document describes best pratices for web crawlers.Discussion Venues   This note is to be removed before publishing as an RFC.   Source for this draft and an issue tracker can be found at   https://github.com/garyillyes/cbcp.Status of This Memo   This Internet-Draft is submitted in full conformance with the   provisions of BCP 78 and BCP 79.   Internet-Drafts are working documents of the Internet Engineering   Task Force (IETF).  Note that other groups may also distribute   working documents as Internet-Drafts.  The list of current Internet-   Drafts is at https://datatracker.ietf.org/drafts/current/.   Internet-Drafts are draft documents valid for a maximum of six months   and may be updated, replaced, or obsoleted by other documents at any   time.  It is inappropriate to use Internet-Drafts as reference   material or to cite them other than as "work in progress."   This Internet-Draft will expire on 10 April 2026.Copyright Notice   Copyright (c) 2025 IETF Trust and the persons identified as the   document authors.  All rights reserved.Illyes, et al.            Expires 10 April 2026                 [Page 1]Internet-Draft                    cbcp                      October 2025   This document is subject to BCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents (https://trustee.ietf.org/   license-info) in effect on the date of publication of this document.   Please review these documents carefully, as they describe your rights   and restrictions with respect to this document.Table of Contents   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2   2.  Recommended Best Practices  . . . . . . . . . . . . . . . . .   3     2.1.  Crawlers must respect the Robots Exclusion Protocol . . .   3     2.2.  Crawlers must be easily identifiable through their user           agent string  . . . . . . . . . . . . . . . . . . . . . .   3     2.3.  Crawlers must not interfere with the normal operation of a           site  . . . . . . . . . . . . . . . . . . . . . . . . . .   4     2.4.  Crawlers must support caching directives  . . . . . . . .   4     2.5.  Crawlers must expose the IP ranges they use for           crawling  . . . . . . . . . . . . . . . . . . . . . . . .   4     2.6.  Crawlers must explain how the crawled data is used and how           the crawler can be blocked  . . . . . . . . . . . . . . .   5   3.  Conventions and Definitions . . . . . . . . . . . . . . . . .   5   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   5   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   6   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   61.  Introduction   Automatic clients, such as crawlers and bots, are used to access web   resources, including indexing for search engines or, more recently,   training data for new artifical 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.   To further assist website owners, it should also be considered to   create a central registry where website owners can look up well-   behaved crawlers.  Note that 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 relationsh with sites, they may exempt themselves from any of   the Crawler Best Practices with a rationale.Illyes, et al.            Expires 10 April 2026                 [Page 2]Internet-Draft                    cbcp                      October 20252.  Recommended Best Practices   The following best practices should be followed and are already   applied by a vast majority of large-scale crawlers on the Internet:   1.  Crawlers must support and respect the Robots Exclusion Protocol.   2.  Crawlers must be easily identifiable through their user agent       string.   3.  Crawlers must not interfere with the regular operation of a site.   4.  Crawlers must support caching directives.   5.  Crawlers must expose the ranges they are crawling from in a       standardized format.   6.  Crawlers must expose a page that explains how the crawling can be       blocked, whether the page is rendered, amd how the crawled data       is used.2.1.  Crawlers must respect the Robots Exclusion Protocol   All well behaved-crawlers must support the REP as defined in   Section 2.2.1 of [REP] 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.2.2.  Crawlers must be easily identifiable through their user agent      string   As outlined in Section 2.2.1 of [REP] (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   descrtion.  For example:   User-Agent: Mozilla/5.0 (compatible; ExampleBot/0.1;   +https://www.example.com/bot.html).   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,   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.Illyes, et al.            Expires 10 April 2026                 [Page 3]Internet-Draft                    cbcp                      October 20252.3.  Crawlers must 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 must ensure that their   crawlers are equped with back-out logic that relies on at least the   standard signals defined by Section 15.6 of [HTTP-SEMANTICS],   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 sourceerrors 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 multle 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 the REP protocol.  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 when JavaScrt runs.   Generally, the load caused by executing JavaScrt should be carefully   considered or even avoided whenever possible.2.4.  Crawlers must support caching directives   [HTTP-CACHING] HTTP caching removes the need of repeated access from   crawlers to the same URL.2.5.  Crawlers must expose the IP ranges they use for crawling   To complement the REP, crawler operators should publish the IP ranges   they have allocated for crawling in [JAFAR] format, and keep this   information reasonably up-to-date, according to the specification.Illyes, et al.            Expires 10 April 2026                 [Page 4]Internet-Draft                    cbcp                      October 2025   The object containing the IP addresses must be linked from the page   describing the crawler, and it must also be referenced in the page's   metadata for machine readability.  For example:   &lt;link rel="help" href="https://example.com/crawlerips.json"&gt;2.6.  Crawlers must explain how the crawled data is used and how the      crawler can be blocked   Crawlers must 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 webpage should also provide an example REP file to block the   crawler and a method for verifying REP files.   If the crawler has exempted itself of these best practices, the   documentation page should describe the reason for that.3.  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 [RFC2119] [RFC8174] when, and only when, they appear in all   capitals, as shown here.4.  Security Considerations   TODO Security5.  IANA Considerations   This document has no IANA actions.6.  Normative References   [HTTP-CACHING]              Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,              Ed., "HTTP Caching", STD 98, RFC 9111,              DOI 10.17487/RFC9111, June 2022,              <https://www.rfc-editor.org/rfc/rfc9111>.Illyes, et al.            Expires 10 April 2026                 [Page 5]Internet-Draft                    cbcp                      October 2025   [HTTP-SEMANTICS]              Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,              Ed., "HTTP Semantics", STD 97, RFC 9110,              DOI 10.17487/RFC9110, June 2022,              <https://www.rfc-editor.org/rfc/rfc9110>.   [JAFAR]    Illyes, G., "A JSON-Based Format for Publishing IP Ranges              of Automated HTTP Clients", Work in Progress, Internet-              Draft, draft-illyes-aipref-jafar-00, 30 September 2025,              <https://datatracker.ietf.org/doc/html/draft-illyes-              aipref-jafar-00>.   [REP]      Koster, M., Illyes, G., Zeller, H., and L. Sassman,              "Robots Exclusion Protocol", RFC 9309,              DOI 10.17487/RFC9309, September 2022,              <https://www.rfc-editor.org/rfc/rfc9309>.   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels", BCP 14, RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <https://www.rfc-editor.org/rfc/rfc2119>.   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.Acknowledgments   TODO acknowledge.Authors' Addresses   Gary Illyes   Independent   Email: synack@garyillyes.com   Mirja Kühlewind   Ericsson   Email: mirja.kuehlewind@ericsson.com   AJ Kohn   Blind Five Year Old   Email: aj@blindfiveyearold.comIllyes, et al.            Expires 10 April 2026                 [Page 6]