Application Programming Interface (API)

An application programming interface (API)An application programming interface (API) is an interface through which software systems communicate and exchange data. It defines how requests are made and answered.Open glossary entry → defines how one system makes functions or data available to another. Applications can exchange information without needing to know each other's internal details.

On the web, APIs are frequently used to load content dynamically, such as product data, prices or search results. The responses are often in the JavaScript Object Notation (JSON)JavaScript Object Notation (JSON) is a lightweight, text-based data format for storing and exchanging data. It is human-readable and easy for machines to process.Open glossary entry → format.

For search engine optimisationSearch Engine Optimization (SEO) covers all measures that help a website become more visible in unpaid (organic) search results.Open glossary entry →, it matters when API data is loaded:

• If content is only fetched client-side via API, it is visible to crawlers only after successful JavaScript renderingJavaScript rendering is the process by which a browser or crawler executes JavaScript code to build the final, visible page. Content that is not already in the delivered HTML only appears after this step.Open glossary entry →.
• Slow, blocked or failing API calls can mean important content is not captured at all.
• Many AI crawlersAI crawlers are automated bots that fetch web pages for AI providers in order to find content, make it available for search functions, retrieve it for answers, or, depending on the provider, use it for model training.Open glossary entry → do not render and therefore often do not see API-based content.

For this reason, SEO-relevant content should be provided server-side where possible and not loaded exclusively via client-side API calls.