How do I contact the owner of a website? Where is a particular website hosted? What other websites are hosted on that same server? Is the site using WordPress or Gatsby? Which ad networks are they using to monetize a site? Is my site accessible from China?

Here are some of the most useful online tools that will help you know every single detail of any website.

Also see: The Essentials Tools for Programmers

• just-ping.com — Use Just Ping to determine if a particular website is accessible from other countries. Just Ping has monitoring servers across the world including Turkey, Egypt, and China so if the ping results say 100% Packet Loss, most likely the site is inaccessible from that region.
• who.is — If you like to know the contact address, email and phone number of the website owner, this free whois lookup service will help. This is a universal lookup service meaning it can simultaneously query the whois database of all popular domain registrars.
• whoishostingthis.com — Enter the URL of any website and this online service will show you the name of the company where that website is hosted. This may come handy if you need the contact information of the web hosting provider for writing a DMCA Notice or if you are looking to switch web hosts.
• chillingeffects.org — When there’s a copyright-related complaint against a website, a copy of that letter is archived in the Chilling Effects database. Anyone can query this public database to know about all the copyright infringement complaints against a particular website.
• myip.ms — MyIP.ms offers a comprehensive report of any website or I.P. Address. You get to know about the hosting provider, the physical location of a website, the IP Address change history of a website and the DNS information. Netcraft also offers similar reports.
• reversewhois.com — The reverse whois lookup will help you determine other websites of someone. You can search the whois database by the email address or name of the domain registrant.
• builtwith.com — Use BuiltWith to know the technology stack of any website. It helps you figure out the mail service provider of a domain, the advertising partners, the tracking widgets that are installed on a website and whether the site is using any CDN like Amazon S3 or Google Cloud. See example.
• ssllabs.com - The certificate diagnostics tool will verify your site’s SSL certificate and ensure that it is correctly installed, trusted and does not show errors to any of your site visitors.
• semrush.com — If you wish to analyze your competitor’s website, this is the tool to go with. SEM Rush will help you figure what organic keywords are people using to find a website, what is the site’s traffic and which are the competing websites.
• dnsmap.io — When you buy a new domain or switch from one host to another, the DNS records for the domain changes and it may take a while to propagate these changes worldwide. The tool checks the DNS records from various geographic locations and it can check your domain’s A, CNAME, TXT and MX records. whatsmydns.net is also a good alternative.
• toolbox.googleapps.com — If email messages, including those sent via Mail Merge, from your domain are not reaching the recipient’s mailbox, use this Google tool to confirm that DMARC, DKIM and SPF records are properly configured for your domain.
• browserstack.com - Check your website’s responsive design on multiple desktops, tables, iOS and Android phones running different versions of operating systems.
• screenshot.guru - If a website is inaccessible, use Screenshot Guru, hosted on the Google Cloud, to confirm if the website is down or not.
• thinkwithgoogle.com - A mobile speed tool developed by Google that will help you determine how fast your websites will load on mobile phones on 3G and 4G network. You can also compare your mobile speed score with other websites.
• testmysite.io - A simple site testing tool from Netlify that will measure and rank your site’s loading time from different regions around the world.
• developers.google.com — Find the Page Speed score of any website on both desktop and mobile devices. The higher this number, the better. The Google tool also offers suggestions on how the score can be improved.
• httparchive.org — The HTTP Archive is a repository of all performance-related metrics for a website. It keeps a record of the size of pages, their average load time and the number of failed requests (missing resources) over time.
• Website Monitor - Use this open-source Google Sheets based website monitoring tool to get alerts when your domain goes down or is inaccessible.
• Flush DNS - Use this tool to flush the Google DNS cache for a domain. If you changed the DNS servers for your domain, by changing registrars or DNS hosting in the last few days, flush your main domain name first before you flush any subdomains. OpenDNS also has a web tool for refreshing the DNS cache.
• DomainTools - The tool monitors one or more web domains and sends email alerts when the domain is expiring, the domain gets renewed, the nameservers change or when the registrant information is updated for the domain.

Also see: 101 Most Useful Websites