Standard being developed on behalf of content publishers to communicate permissions information more extensively than is the case with robots.txt. Project documents, implementation and background information.

Search Tools Consulting explains how the search engine programs called "robots" or "spiders" work, and reviews related sites.

This large database lists user agents in categories and distinguishes between robots and browsers.

An alphabetical list of user agents and the deployer behind them, compiled by Christoph Rüegg.

A list from PGTS of Web robots with the identifying data they leave in Web site logs.

Brian Dunnintg provides a list of all the major search engine robot IP addresses, by full class C only.

Information on the robots.txt Robots Exclusion Standard and other articles about writing well-behaved Web robots.

Lists IP addresses of search engine spiders. Can be searched by IP address. Also links to resources on spiders.

John A. Fotheringham presents data in tabular form on the robots sent by search engines and other sites to read and index Web pages: their origins, names and IP addresses.

Tool from ASAP Consulting s.r.o. for detailed user agent string analysis using an online form. Includes databases of browsers and robots.