7 free services for checking sites (which you might not know about)

Quite often I have to use various online services to check the availability of sites and their surface tests and checks.
As a brief survey of colleagues showed, almost all of these sets of services differ. I want to show you mine, please.

LoadImpact: http://loadimpact.com , a site load testing service (for money - up to 5k simultaneous connections) which has a free test for 50 simultaneous connections. If you host a ruthless and merciless domestic hoster for $ 0.01 / month and you have only a thousand sites on the server - try to check your own, with a high probability it will not even withstand 50 simultaneous connections.

BrowserMob: http://browsermob.com, an additional simple but nice service that allows you to check the download speed of the target site from 4 different places and showing a lot of detailed download metrics for each of them. And the main task of BrowserMob is automatic cross-browser testing of sites.

Alertra: http://alertra.com , an uptime monitoring service on the site of which you can check the availability (and response time) of a site from 11 different places for free. It works quickly and reliably, no captcha and other rubbish.

site24x7: http://site24x7.com , an Alertra-like service that already uses 23 geographically distributed checkpoints.

You get signal: http://www.yougetsignal.comAn excellent service that allows you to check open ports on any host / IP. Often helps to check port forwarding through NATs.

Now let's move from accessibility checks to a little more complicated things. I won’t write about w3c products, I hope everyone knows and uses them anyway.

CSE HTML Validator: http://www.onlinewebcheck.com is an alternative to the well-known validator.w3.org , built [apparently] on its own separate analysis core. It compares favorably with very detailed and understandable recommendations for fixing errors and potential problems.

Built with: http://builtwith.com/analyzes a given site and issues a whole dossier about it: a web server, CMS, which statistics service is used, and so on. There are a lot of indicators, it is quite suitable for a cursory analysis of competitors. Also, it is interesting to delve into trends.builtwith.com where service owners issue statistics for all monitored parameters. For example, the vast majority of sites still use the old blocking JS code for Google Analytics.

And what services do you have in your bookmarks?