The primary data format used in GraphQL APIs is JSON (JavaScript Object Notation). JSON is a lightweight and human-readable format, making it well-suited for data exchange between clients and GraphQL servers. GraphQL can also work with other data formats, but JSON is the most common.

Automating API tests offers several benefits, including faster test execution. Automated tests can be run more frequently and consistently than manual tests, helping to identify issues early in the development process and saving time and resources. Automated testing can also provide more comprehensive test coverage.

API keys are just one method of authentication. Alternatives include using token-based authentication, such as OAuth. OAuth provides a robust, secure, and standardized approach to authentication and authorization. Using a personal name as a password or leaving endpoints unsecured are not recommended security practices.

Rate limiting in a Web API is implemented to protect against abuse and ensure fair usage. It limits the number of requests that a client can make within a specified time frame, preventing overuse and ensuring that resources are available for all users. This helps maintain the quality of service and prevents misuse.

The REST (Representational State Transfer) architectural style for Web APIs uses a stateless communication mechanism, ensuring that each call from a client to a server is treated as a new request. RESTful APIs are known for their simplicity and scalability.

Automated testing for APIs can present challenges in terms of limited scalability, as maintaining test automation can become complex as the number of APIs grows. It is essential to ensure that the test automation framework can handle the increasing number of API endpoints and scenarios.

The purpose of debugging in API development is to identify and fix issues or errors in the API code and functionality. Debugging helps ensure that the API works as intended, and it is a critical step in the development process to deliver a reliable and error-free API to users. Debugging does not aim to introduce errors, enhance security, or slow down the API.

API security concerns include protecting against unauthorized access, SQL injection, and data breaches. SQL injection is a type of attack where an attacker injects malicious SQL code into input fields, potentially compromising the database and exposing sensitive information.

To keep the user interface updated in a social media application using GraphQL, you should use GraphQL subscriptions. Subscriptions enable the server to push real-time updates to clients over WebSocket connections, providing efficient and responsive real-time communication.

OAuth 2.0 is primarily used for authentication and authorization in web applications. It allows a user to grant limited access to their resources on one site to another site without sharing their credentials. It is commonly used for user authentication and secure data access between different web applications.