Explained

How things work, with a diagram first and the reasoning after. Each page ends with a way to make your own version in chat.

Web and security

How OAuth login works

What happens when you click Sign in with Google: the redirect, the one-time code and the tokens, as a sequence diagram.

How HTTPS works

What happens between your browser and a website before any data is sent: the certificate check and the shared key, as a diagram.

How DNS works

How your computer turns example.com into an IP address, with the resolver, root, top-level and authoritative servers in a diagram.

How JWT authentication works

How a signed token replaces a server-side session: login, the token, and how each request is checked, in a diagram.

Architecture

How file uploads to S3 work

The safe way to upload large files from a web app to S3: a presigned URL from your server, then a direct upload from the browser.

Monolith vs microservices

A side-by-side comparison of one deployable application and many small services, and why most small teams should start with a monolith.

How caching works

How a request is answered from the closest layer that already has the answer, with browser, CDN, app and database caches in a diagram.

Teamwork and process

How a CI/CD pipeline works

From a pushed commit to a running release: build, test, package and deploy, as a simple flow.

Agile vs waterfall

A side-by-side comparison of planning everything first and delivering in small steps, and when each one is the right choice.

Money

How compound interest works

Why money grows faster over time: interest earns interest. A worked example and the four things that matter most.

How a loan is repaid

Why the first payments are mostly interest and the last ones mostly principal, and what a shorter term or an extra payment changes.

Restaurants

How to create a QR code menu for your restaurant

Five steps from your dishes to a QR code on the tables: build the menu page, make it read well on a phone, add allergens, print the code and keep it current.