Site Info - Duolingo.com

Content Management Systems

Shopify is a hosted online store building service.

Ghost is an open source publishing platform built on Node.js, originally developed by John O'Nolan.

Atlassian Statuspage is a hosted service for showing the status of services.

Server-side Programming Languages

Ruby is a general-purpose object-oriented language originally developed by Yukihiro "Matz" Matsumoto in Japan.

JavaScript is a lightweight, object-oriented, cross-platform scripting language. This includes TypeScript.

Client-side Programming Language

JavaScript is a lightweight, object-oriented, cross-platform scripting language, often used within web pages.

JavaScript Libraries

jQuery is a JavaScript library that simplifies HTML document traversing, event handling, animating and Ajax interaction. Originally developed by John Resig.

Moment.js is a library to manipulate dates in JavaScript.

MathJax is a JavaScript engine for displaying mathematical formulas.

CSS Framework

Bootstrap is an open source HTML, CSS, and JavaScript framework.

Web Servers

Envoy Proxy is a proxy server designed for large service-oriented architectures.

Nginx (pronounced as "engine X") is a lightweight open source web server developed by Igor Sysoev.

Cloudflare Server is a web server developed by Cloudflare.

Node.js is a server-side JavaScript environment for writing network programs such as web servers, originally developed by Ryan Dahl.

Web Hosting Providers

Amazon is a US-based e-commerce and cloud computing provider.

Shopify is a hosted online store building service.

Atlassian offers a range of IT products and services.

Data Center Provider

Amazon is a US-based e-commerce and cloud computing provider.

Reverse Proxy Services

Amazon CloudFront is a content delivery web service by Amazon.

Cloudflare provides a content delivery network.

Fastly is a content delivery network.

DNS Server Provider

Amazon is a US-based e-commerce and cloud computing provider.

Email Server Provider

Gmail is the email service provided by Google.

SSL Certificate Authorities

Starfield Technologies is an SSL certificate authority owned by Go Daddy.

Let’s Encrypt is a free, automated, and open certificate authority provided by the Internet Security Research Group.

GlobalSign is an IT security service provider, also operating as SSL certificate authority.

Sectigo (formerly Comodo CA) is a US-based SSL certificate authority.

JavaScript Content Delivery Networks

The CDNJS is a content distribution network, hosting a large number of JavaScript libraries, provided by CloudFlare.

jsDelivr is a service for hosting JavaScript files.

The jQuery CDN hosts copies of the jQuery library, provided by MaxCDN.

unpkg is a JavaScript content delivery network for libraries that use the npm package manager.

Traffic Analysis Tool

Google Analytics is a free service to get detailed statistics about the visitors of a website, provided by Google. This includes the Ads conversion tracking and the Floodlight services.

Advertising Network

The Google Advertising network consists of AdSense, DoubleClick and other services.

Tag Manager

The Google Tag Manager is a Google service to support webmasters to manage tags on their websites.

Social Widgets

The WhatsApp share button allows users to share content with their WhatsApp contacts.

Facebook Social Plugins provide a way for Facebook users to share web pages with their friends.

A Twitter/X Button allows a Twitter user to post a tweet from the visited site.

LinkedIn Share Buttons enable visitors to to share website content with their LinkedIn network.

Site Elements

External Cascading Style Sheets define style rules in a separate CSS file.

Embedded Cascading Style Sheets define a set of style rules in a <style> element within a web page.

Inline Cascading Style Sheets define style rules directly within an (X)HTML element using the style attribute.

Session cookies are temporary cookies, which are deleted when the user closes the browser.

Persistent cookies with an expiration time between 1 day and 1 month.

Persistent cookies with an expiration time between 1 month and 1 year.

Non-HttpOnly cookies are used in the HTTP protocol and also in client side scripts, which may be a security threat.

Secure cookies are used only via an encrypted connections, which may increase security.

Non-secure cookies may be used via an unencrypted connections, which may be a security threat.

Gzip (GNU zip) is a file compression algorithm.

Brotli is a lossless compression algorithm developed by Google.

A strong ETag is an HTTP header field for validation of cached web pages, that indicates a byte-for-byte identical page in the cache.

A weak ETag is an HTTP header field for validation of cached web pages, that indicates a semantically equivalent page in the cache.

The Internet Protocol version 6 (IPv6) provides amongst others a vastly larger address space than the preceding version 4. We consider a website to support IPv6 if a 128-bit address is assigned to it, regardless of the content delivered at that address.

HTTP/2 is the second major version of the HTTP network protocol.

HTTP/3 is the third major version of the HTTP network protocol, derived from the QUIC protocol.

HTTP Strict Transport Security (HSTS) defines a mechanism enabling web sites to declare themselves accessible only via secure connections.

The websites redirects visitors to its www subdomain, e.g. from example.com to www.example.com.

The websites redirects visitors to use SSL encryption, e.g. from http://example.com/ to https://example.com/.

Structured Data Formats

The Open Graph protocol, originally developed by Facebook, is an RDFa-based format that enables any web page to become a rich object in a social graph.

Twitter/X Cards enable automatic attachment of photos, videos and media elements to tweets.

Generic RDFa (Resource Description Framework in attributes) is RDFa without further specialization.

JSON-LD (JavaScript Object Notation for Linked Data) is a method of encoding Linked Data using JSON.

Microdata is a specification to integrate metadata within existing content on web pages.

Markup Language

HTML5 is the fifth revision of the HTML standard.

Character Encoding

UTF-8 (8-bit Unicode Transformation Format) is a variable-length character encoding for Unicode, which is backwards compatible with ASCII.

Image File Formats

Scalable Vector Graphics (SVG) is an XML-based vector image format.

PNG (Portable Network Graphics) is a lossless compression image format, suitable to store graphics with uniformly colored areas, and originally introduced as a free, open-source successor of GIF.

JPEG (Joint Photographic Experts Group) is a lossy compression method suitable to store photographic images.

Top Level Domain

Commercial entities

Server Locations

Content Language