Understanding Configuration File Formats
Each configuration format has unique characteristics and is suited for different use cases. Understanding these differences helps you choose the right format for your project.
JSON (JavaScript Object Notation)
JSON is a lightweight, hierarchical data format that supports nested objects and arrays. Widely used for web APIs and modern applications, JSON provides strict syntax with excellent tool support. However, it doesn't support comments and requires quoted strings, which can make it less human-friendly for configuration files. Best for: Structured configs with nested data, API responses, cross-language compatibility.
TOML (Tom's Obvious, Minimal Language)
TOML is a modern configuration format designed to be easy to read and write. It supports sections (tables), nested structures, and comments, making it ideal for application configs. TOML uses clear key-value syntax and is less verbose than JSON while being more structured than INI. Popular in Rust, Python, and modern tooling ecosystems. Best for: Application configs, package manifests (like Cargo.toml), human-editable settings.
INI (Initialization File)
INI is a simple, legacy configuration format consisting of sections and key-value pairs. Widely used in Windows applications and older systems, INI files are easy to read but lack standardization. They don't support nested structures or complex data types, limiting their use to flat configurations. Comments use semicolons or hash symbols. Best for: Simple configs, legacy Windows applications, flat key-value settings.
ENV (.env File)
ENV files store environment variables as simple KEY=VALUE pairs, one per line. Commonly used in Docker, Node.js, and 12-factor apps, ENV files are perfect for environment-specific settings. They don't support nested structures, sections, or complex data types, making them ideal for flat configuration. Comments use hash symbols (#). Best for: Environment variables, Docker configs, deployment-specific settings, secrets management.
Properties (.properties File)
Properties files are Java's native configuration format, using simple key=value or key:value syntax. They support Unicode escaping for international characters and can span multiple lines using backslash. While flat in structure, properties support hierarchical naming through dot notation (e.g., database.host). Comments use hash (#) or exclamation mark (!). Best for: Java applications, internationalization (i18n) resource bundles, JVM-based systems.