Domains and DNS: names for addresses
A domain is a memorable name. DNS queries resolve names to addresses and other records. Browsers and operating systems may cache answers, so not every visit requires a fresh external query.
A complete URL also includes a scheme, path, and possibly other parts. In https://example.com/notes, the domain helps find the service while /notes identifies a resource. HTTPS adds encrypted communication and authentication mechanisms.
When name resolution fails, the request hasn't reached the intended site normally. Examining database rows is unlikely to be the first useful step.
Take this with you · Provide the full URL instead of saying only “that website.”
A request goes out, a response comes back
The browser acts as a client and sends an HTTP request. The server returns a status code, headers, and a body. The body might contain HTML, JSON, an image, or something else.
The browser parses HTML and may request scripts, styles, and images. HTML describes structure, CSS presentation, and JavaScript behavior. A webpage is not simply a fixed picture.
Opening a list and pressing Load more may create separate requests. The initial page working doesn't mean every later request succeeds.
Take this with you · Ask what was requested, what came back, and how the interface handled it.
Forms and status codes
Submitting a form can send input to a server for validation, processing, and storage. The response tells the interface what happened. A success message should reflect a real outcome, not just a click.
200 generally indicates success; 404 means the requested resource wasn't found; 500 indicates an internal server error. Codes provide clues, not complete diagnoses. A 500 alone doesn't prove a database fault; inspect the response and logs.
For a failed save, report the operation, endpoint, status, and error text. Don't ask AI to rebuild a database based on one status code.
Take this with you · Report evidence and leave the cause open to investigation.
Follow a request there and back
Choose a server scenario and send a simulated request. Watch its path and response status.
GET /notes HTTP/1.1…Try both a missing resource and a processing error.
Responses are produced by local scenarios, not real servers. A status code is not an automatic root-cause diagnosis.
Make your project reachable
Local running is mainly for development and checks. Deployment places built content or a service in an environment reachable by its intended users, with the necessary configuration and availability.
Static pages can be distributed through static hosting or a CDN. Server-side logic needs a compatible runtime. A server is a role, which may be fulfilled by a physical machine, virtual machine, or managed environment.
Sending someone an exported HTML file delivers a file. Deploying it and sharing a URL delivers online access. Updating it and storing user data work differently.
Take this with you · Check both “I can open it” and “the intended user can use it.”
Deciding what a provider manages
IaaS supplies infrastructure with more system work left to you. PaaS supplies an application platform. SaaS offers software you use as a service. Real products can span these categories.
Databases, identity, and file storage also come as managed services. Focus on who runs the system, owns backups, handles access, and pays the costs rather than memorizing labels.
A personal list may only need local saving. Shared use can later introduce accounts, a database, and access controls.
Take this with you · Choose services from the actual requirements of your first version.
Submitting a form returns 500. Which statement is most accurate?
Choose an answer before reading the explanation.
Describe a failed save in a way that supports investigation and verification.
Think first, then uncover help as needed. Later chapters expect more complete descriptions and clearer checks.
Bring this chapter's context to your AI. Going deeper is optional; you can keep reading without it.
Connect DNS, HTTP, HTML, and browsers in a restaurant analogy, including its limits.
One approach you can make your own
I'm learning computers and AI-assisted programming from scratch. In this chapter I learned: Internet：Explain domains, DNS, HTTP, and the browser's role；Distinguish an unreachable service, a 404, and a server error；Understand local development versus access for other people Connect DNS, HTTP, HTML, and browsers in a restaurant analogy, including its limits. Check my understanding first. Explain one small question at a time with a concrete example and the limits of any analogy. Ask a scenario question, then adapt to my answer. Distinguish facts, guesses, and uncertainty; suggest hands-on ways to check. Confirm the version before giving tool-specific advice, and don't invent features or references.
Complete this chapter
Mark the sections as read, finish the experiment, and pass the scenario check to record completion. You can visit the next chapter at any time.
Read the original references
This is an introduction. These official resources help you check details and explore further.
MDN · How the web worksMDN · Client-server overviewRequests move information. Next, find out where information is stored and how to retrieve it correctly.