Javadoc is a tool provided by Oracle for generating API documentation in HTML format directly from Java source code. It is an integral part of Java development, offering a standardized way to create user-friendly, structured documentation for classes, methods, fields, and packages. By embedding descriptive comments in the code, developers ensure that the generated documentation is tightly aligned with the actual implementation.

How It Works:

- Annotation Syntax: Developers use special comments, called Javadoc comments, enclosed by /** and */. These comments describe the functionality of methods, classes, and fields. They can include markup tags like @param (to describe parameters), @return (to specify return values), @throws (to document exceptions), and @see (for cross-references).

- Generating Documentation: By running the javadoc command-line tool, annotated source files are processed to generate a set of interlinked HTML pages. These pages detail the structure and behavior of the application or library.

Key Advantages:

1. Improved Clarity: Helps developers understand the purpose and usage of code elements, making APIs intuitive for other programmers.
2. Ease of Maintenance: By embedding documentation within the source code, developers ensure that updates to code are reflected in the documentation, reducing inconsistencies.
3. Customizability: Developers can add custom tags and styles to suit specific project requirements.
4. Community and Open Source: Many open-source Java libraries rely on Javadoc to provide users with clear, detailed, and easily accessible API documentation.

Best Practices:

- Write concise, clear descriptions.
- Use proper formatting and tags to enhance readability.
- Keep documentation up to date with code changes.

Javadoc's consistency and integration with Java tools and IDEs make it indispensable for both small and large-scale Java projects.