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Browse all articles and guides on network tools, programming and online security.
Robots.txt guide
Everything about the robots.txt file — syntax, directives, examples, and common mistakes.
SSL errors
Meet the most common SSL/TLS errors and learn how to diagnose and fix them.
DNS errors
Meet the most common DNS errors and learn how to diagnose and fix them.
Secure passwords
Learn how to create strong passwords, what to avoid, and how to use a password manager.
Page Header Structure
Learn what HTML headings H1-H6 are, how to build a correct hierarchy, how they affect SEO and accessibility, and how to check the heading structure of your page.
DNS Record Information
Learn all DNS record types: A, AAAA, CNAME, MX, TXT, NS, PTR and others. Find out what TTL, SPF, DKIM, DMARC are and how to check your domain's records.
Text formatting styles
Learn the most popular text writing styles used in programming and SEO: camelCase, PascalCase, snake_case, kebab-case and others.
What is an IP address / IPv4 / IPv6?
Learn how to check your IP address, what the difference between IPv4 and IPv6 is, and how to check your location and internet provider.
HTTP Codes List
Complete reference of HTTP response codes (200, 301, 404, 500 and more). Learn what they mean and how they affect your website.
What is an SPF record?
Everything about SPF records. Learn how to protect your domain from spoofing and improve email deliverability.
Errors in SPF records
Learn why an SPF record may return a fail or permerror. We explain the most common issues and how to fix them.