JSON vs XML vs YAML vs TOML — Config Format Comparison

July 13, 2026

Configuration and data serialization formats are the backbone of modern software development. Every application needs a way to store, transmit, and structure data. JSON, XML, YAML, and TOML are the four most popular formats, each with distinct design philosophies, strengths, and ideal use cases.

Choosing the right format affects developer experience, parsing performance, file size, and long-term maintainability. Whether you are designing a REST API, writing application configuration, defining CI/CD pipelines, or serializing data for storage, understanding the differences between these formats helps you make an informed decision. This configuration format comparison covers everything you need to know.

Should I use JSON or YAML for my config file? ▼JSON if you need speed and cross-language compatibility. YAML if humans will edit the file directly. JSON is stricter and parses faster. YAML is easier to read and supports comments, but its indentation can cause tricky bugs.Is XML dead? ▼Not dead, but it has retreated to its strongholds: enterprise software, SOAP services, Android layouts, SVG, and Office documents. For web APIs and app config, JSON and YAML have taken over.When would I pick TOML over YAML? ▼When you want something simple and unambiguous. TOML is great for project config files like Cargo.toml or pyproject.toml. YAML is better when you need complex nested data, anchors to avoid repetition, or multi-document files.Why does JSON not support comments? ▼By design. JSON was built for machine-to-machine data exchange, not human-edited config files. If you need comments, use YAML, TOML, or JSON5.Which format parses the fastest? ▼JSON, by a wide margin. Its simple syntax means parsers are tiny and blazing fast. XML is slower due to namespaces and schemas. YAML is the slowest because its spec is huge and parsers have to handle indentation, anchors, and type detection.