JSON vs YAML: which data format should you use for configs, APIs, and devops?

How this is calculated

JSON's strength is its simplicity: six data types, no surprises, every parser produces the same result from the same input. It's the native format of REST APIs and the lingua franca of web development. YAML's strength is its readability for humans: significant whitespace, comments, multi-line strings, and anchors that let you reuse configuration blocks. The trade-off is that YAML's spec is enormously complex (the 1.2 spec is 84 pages) and different parsers can interpret the same YAML differently, which has led to security vulnerabilities in Kubernetes and Ansible.

Verdict

The technical basis for the split is parser determinism. JSON's six-data-type grammar is small enough that every parser produces the same result from the same input, which is non-negotiable for APIs and machine-to-machine data interchange. YAML's 84-page 1.2 spec allows significant whitespace, anchors, aliases, and multi-document files, with the cost that two parsers can interpret the same YAML differently, which has been the root cause of real CVEs in Kubernetes and Ansible. The trade makes YAML the right call for human-edited infrastructure configs (where readability and comments matter more than parser portability) and JSON the right call for everything machine-facing. TOML's case as the app-config middle ground is its narrower grammar, which keeps comments and human readability without YAML's parser-ambiguity risk.