Wikipedia:Administrators' guide/Blocking/Tools

Twinkle – A comprehensive block+template tool. Allows you to choose a preset that auto-supplies the standard block duration, block summary, and template to issue to the user. You will see different presets and options when blocking IPs versus accounts. You can also use this gadget just to template the user and not block, and vice versa. If the user has been blocked in the past, a link to the block log will be shown. Also automatically disables a hard block when blocking bots.
EasyBlock – Block+template script with numerous options on types of blocks. This is quicker than Twinkle but does not allow you to choose block options. Many admins use both scripts.
- EasyBlock-modern – Same as the above, but tweaked to work on the Modern skin.
massblock – Block multiple users at once. Use with caution!
Note you can also block while patrolling recent changes with Huggle

Domaintools – Probably the most comprehensive of the WHOIS tools, however requires you enter a CAPTCHA and has a limit of about 50 lookups a day. Be sure to check not just the ASN but the network name, etc, when attempting to determine if an IP belongs to a school or is otherwise shared.
Whois Gateway on labs – free, CAPTCHA-less and limitless WHOIS lookups for IPs. May not show the network name in some situations.
Betacommand's WHOIS tool – returns the ASN and CIDR range for an IP, checks for global blocks and returns the block log. To use, append the IP to the URL like ?ip=1.2.3.4
For an up-to-date list of the most commons tools used when checking IPs, refer to {{anontools}}, passing it an IPv6 address if needed.

Range contributions are now supported in MediaWiki core. Simply enter the range at Special:Contributions.

You can also do a wildcard search (e.g. 83.217.178.*) using the Contribsrange gadget gadget. Enable "Allow /16, /24 and /27 – /32 CIDR ranges" at Special:Preferences#mw-prefsection-gadgets under "Advanced". Then type in any CIDR range into Special:Contribs.