How Browsers Work

Summary

An interactive guide that walks through the complete browser pipeline: URL processing, HTTP requests, DNS resolution, TCP connections, HTML parsing, DOM construction, and the rendering pipeline. The hands-on examples let you experiment with each stage.

Key Concepts

The Browser Pipeline

1. URL Processing — Normalizes user input into proper URLs
2. HTTP Request — Converts URLs into HTTP requests with headers
3. DNS Resolution — Translates domain names to IP addresses
4. TCP Connection — Establishes reliable three-way handshake
5. Request/Response Cycle — Data exchange between browser and server
6. HTML Parsing — Builds the DOM tree from raw HTML
7. Rendering — Layout, painting, and compositing to display pixels

The DOM's Central Role

The Document Object Model sits at the center of browser functionality. JavaScript manipulates it, CSS styles it, and the rendering engine paints it. Every performance optimization eventually traces back to DOM operations.

Visual Model

flowchart LR
    URL[URL Input] --> HTTP[HTTP Request]
    HTTP --> DNS[DNS Lookup]
    DNS --> TCP[TCP Handshake]
    TCP --> Response[Server Response]
    Response --> Parse[HTML Parser]
    Parse --> DOM[DOM Tree]
    DOM --> Render[Render Tree]
    Render --> Layout[Layout]
    Layout --> Paint[Paint]
    Paint --> Composite[Composite]
    Composite --> Pixels[Pixels on Screen]

Why This Matters

Building a mental model of browser internals pays dividends when debugging. Slow page? Now you know whether the bottleneck is DNS, parsing, layout, or painting. Understanding the pipeline helps you write code that works with the browser instead of against it.

Connections

No directly related notes exist in this knowledge base yet. This note serves as a foundational reference for future content about web performance, rendering optimization, or browser APIs.