Fine-tuning the granularity of API throttling can ensure that resources are not overused while still providing a responsive service. Granularity refers to the level of detail at which you set throttling limits. By defining specific limits for different types of requests, you can optimize resource allocation.

ASP.NET Core is primarily used for building server-side web applications. It's a cross-platform, high-performance framework that enables developers to create robust, scalable, and efficient web applications that can run on Windows, Linux, and macOS. It's not focused on client-side JavaScript, mobile app development, or database management.

API key rotation is a practice where API keys are periodically regenerated to enhance security. This process involves generating new API keys to replace the old ones, reducing the risk of unauthorized access and misuse of keys. It's a vital security measure to protect APIs.

Keeping API keys secure is crucial to prevent accidental exposure. Exposed API keys can lead to unauthorized access, data breaches, and potential misuse of your API services, compromising the security of your applications and data.

Common strategies for API versioning include URL versioning (e.g., "/v1/endpoint"), header versioning (e.g., specifying the version in HTTP headers), and content negotiation (accepting different response formats based on version). These methods allow for evolving APIs while maintaining compatibility.

The goal of API monitoring and analytics is to continuously track an API's health and usage, detect issues, and analyze data for insights. It helps ensure reliability, security, and performance while optimizing resource allocation.

ASP.NET Core ensures the scalability and performance of APIs through support for asynchronous programming. This allows APIs to handle a large number of concurrent requests efficiently by not blocking threads, making it suitable for high-demand scenarios.

The "Content-Type" header in an HTTP request can be used to specify the format of the data being requested from a Web API. It indicates the media type (e.g., JSON, XML) of the data being sent or received, allowing the server to process the request appropriately.

During API development, testing tools can help identify issues such as endpoint errors or data inconsistencies. These tools are crucial for detecting and addressing problems in the API's functionality, ensuring that it behaves as expected and delivers the correct data. Effective testing tools can include unit testing frameworks, integration testing, and automated testing suites.

When designing a Web API, considerations such as "endpoints," scalability, and security are crucial. Endpoints represent the different paths or URLs that clients can access to interact with the API, making them a key component in the design of a Web API.