Microsoft Edge Add-ons is Microsoft's online store for add-ons to the Edge browser: extensions and themes. An extension is a small app that adds or changes features of the browser or of specific web pages, such as an ad blocker or a password manager. It contains a manifest JSON file with basic information (name, description, permissions), JavaScript code, and HTML and CSS files for its user interface.
Edge is based on Chromium, the open-source browser project that Google Chrome, Opera and Brave also use, and these browsers share the same extension APIs and packaging, so in most cases a Chromium extension works in all of them. A developer registers for the Microsoft Edge program at Partner Center with a Microsoft account, uploads the extension as a .zip package, chooses public or hidden visibility and the markets, and declares the extension's single purpose, its permissions and its data use. Microsoft then certifies the submission, which can take up to seven business days; after it passes, the extension is published in the store.
Publishing is free: Microsoft charges no registration fee for submitting extensions.