Here is a list of the online tools I use, which might be helpful for you to find out if your website is without bugs or if it has some greater problems. Have fun and take a look at your own website.
Last updated November 11, 2019.
During my development at Blogless and mobiki I came across the question in many areas whether I am doing everything right. Sometimes you think you've understood everything, but it's always good to see if a programming or approach is really correct. Are all HTML tags correct, is my CSS stylesheet correct, does my international language version “hreflang” match?
Generic online validation tools
- W3C Markup Validation Service - shows you if your HTML is correct
- NU HTML Checker - the same, but more modern and still experimental
- W3C CSS Validation Service - for validating your CSS stylesheets
- W3C Feed Validation Service - shows you if the RSS feed you created is set up correctly
- Validome Sitemap Validator - check if your sitemap.xml is ok.
- Sistrix hreflang Validation - shows if your website has correct international language information
Specific validation tools for metadata
- Google's Structured Data Testing Tool - for Schema.org Awards
- Twitter Card Validator - checks your Twitter Card-Meta Information
- Facebook Open Graph Debugger - checks Open Graph meta information (account required)
- IndieWebs h-entry Validator - if you use Microformats.
Validation regarding security
- Observatory of Mozilla - checks your website for security
- CSP Analysis by Report Uri - analyzes and builds a content security policy for you
- SSL Server Test from Qualsys SSL Labs - Check your SSL Settings
- Hardenize - Checks your web server and several DNS settings
- hstspreload.org - checks if your domain is configured correctly for HSTS
- WebSec - Test your Content Security Policy (CSP), HTTP Security Headers and Web Server Security
Speed and other tools
- HTTP Compression Test - Tests if your web server compresses the output gzip.
- Pingdom Website Speed Test - Tests how fast your site loads
- Google Pagespeed Insights - Measures time to drawing and first usability of the page
Mail Server Validation
- SMTP Diagnostics - Check your mail servers base configuration
- Mail Tester - Receives mails and guesses your spam level
I will add to this list as soon as I encounter more cool tools