Design attributes on custom Lightning components
Key Takeaway
Design attributes let an admin adjust a coded component with clicks, but builder tools don't all honor the same settings.
Design attributes are the settings a developer exposes on a custom Lightning component so an admin can change them in a builder tool such as the Lightning App Builder. The developer defines them in the component's files. The admin then sets their values with clicks in the properties pane, which adjusts the coded component on a page.
Custom Lightning components on a page
A developer can build a custom Lightning component with Aura or Lightning Web Components (LWC), which takes programming skills. An admin can also install an existing component from AgentExchange.
Either way, a custom component doesn't automatically work on Lightning pages. It must be configured for the Lightning App Builder before it shows up in the Lightning Components pane. When the admin works with the component on a page, its design attributes appear in the properties pane.
For example, an Opportunity Alert component can expose a Days Since Last Modified value and a Has Open Tasks option. When the admin changes the value, the text in the component updates to match.