Crawler best practices
draft-illyes-aipref-cbcp-00
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| Authors | Gary Illyes , Mirja Kühlewind | ||
| Last updated | 2025-07-07 | ||
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draft-illyes-aipref-cbcp-00
Network Working Group G. Illyes
Internet-Draft Independent
Intended status: Informational M. Kuehlewind
Expires: 8 January 2026 Ericsson
7 July 2025
Crawler best practices
draft-illyes-aipref-cbcp-00
Abstract
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
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This Internet-Draft will expire on 8 January 2026.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Recommended Best Practices . . . . . . . . . . . . . . . . . 2
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 . . . . . . . . . . . . . . . . . . . . . . . . . . 3
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 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 . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Automatic clients, such as crawlers and bots, are used to access web
resources, including indexing for search engines or, more recently,
for new artificial intelligence (AI) applications like training
models. 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 relationship with sites, they may exempt themselves from any of
the Crawler Best Practices with a rationale.
2. 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.
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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 IP ranges they are crawling from in a
standardized format.
6. Crawlers must expose a page that explains how the crawled data is
used and how it can be blocked.
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
description. 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.
2.3. 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 equipped 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
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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.
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 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 JavaScript runs.
Generally, the load caused by executing JavaScript 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 a standardized, machine-readable
format, and keep this information reasonably up-to-date (i.e., should
not be outdated for more than 7 days).
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:
<link rel="help" href="https://example.com/crawlerips.json">
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2.6. Crawlers must explain how the crawled data is used and 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.
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 Security
5. 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>.
[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>.
[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>.
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[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
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