semrush.com — If you wish to analyze your competitor’s website, this is tool to go with. SEMrush 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.
whatsmydns.net — When you buy a new domain or switch from one host to another, the DNS records for the domain change and it may take a while to propagate these changes worldwide. WhatsMyDNS check your DNS records from various locations and it can check your domain’s A, CNAME and MX records.
modern.ie — This online app will help test your website’s compatibility with various web browsers and detects coding errors that might cause problems. The site is integrated with BrowserStack so you can quickly know how your site looks on different devices and browsers.
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 suggestion on how the score can be improved.
ctrlq.org/sandbox — The AdSense sandbox solves two problems – it shows the various advertisers that are targeting a website and it will also help you figure out if a particular web domain is banned in the AdSense network or not.
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.
just-ping.com — Use Just Ping to determine if a particular website or blog is accessible from other countries. Unlike other online ping services that have service in a couple of locations, Just Ping has 30 monitoring stations across the world including Turkey, Egypt and China. 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 handl if you need the contact information of the web hosting provider for writing aDMCA Notice or if you are looking to switch web hosts.
popuri.us — You can use popuri to estimate the relative popularity of a website on social sites like Twitter, Google+ and Facebook. It also display the Google Pagerank of a website and the Web of Trust matrix.
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.
ewhois.com — Ewhois, short for enhanced whois lookup, will help you determine other websites of someone. It looks the whois details, the AdSense publisher ID and the Google Analytics code of websites to figure out other web domain that may belong to the same owner.
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.