Localhost seems simple, but in real projects it often becomes a source of confusing and hard-to-debug issues.

Why does a service work without internet access? Why does localhost fail while 127.0.0.1 works? And why do tests suddenly break in CI or Docker environments?

In this article, we explain how localhost actually works at the operating system level, what loopback really means, and why modern systems may resolve localhost to IPv6. The article focuses on practical scenarios and common pitfalls that QA engineers and developers face when working with local environments, automated tests, and containerized setups.

HTTP status codes are one of the core communication mechanisms of the web, yet in practice they are often treated as secondary details. Many applications rely on response bodies to signal errors or success, while status codes are used inconsistently or even contradict the actual result of request processing.

In this article, I take a closer look at HTTP status codes as protocol-level signals and explain why their semantic correctness matters for web and API testing. The discussion covers the main status code classes, common inconsistencies between status codes and response bodies, and how these issues affect client behavior.

The article also includes a real-world case study discovered during server analysis, where a redirect response appeared safe in the browser but still exposed private data to non-browser clients. This example highlights why browser behavior cannot be trusted as the only validation method and why protocol-level inspection is essential when testing web systems and APIs.

crt.sh is a widely used tool in security research and OSINT that provides visibility into SSL/TLS certificates published through Certificate Transparency logs. By working with publicly issued certificates, it helps uncover subdomains, map hidden infrastructure, and monitor certificate activity across domains.

Its simple interface hides a powerful data source that can reveal forgotten services, internal environments, and unexpected relationships between domains.

Authentication and authorization are two core security processes that work together to protect systems and data. Authentication focuses on verifying a user's identity, while authorization defines what resources and actions that user is allowed to access. Understanding this distinction is crucial for building strong security.

A useful analogy is an airport: first, a passenger's identity is confirmed, and only then are their privileges determined – such as boarding class or lounge access. In digital systems the logic is the same. Authentication ensures users are genuine, and authorization grants specific permissions based on roles and policies. Proper configuration of both mechanisms is essential for any secure environment.