JSON vs YAML
JSON and YAML are the two most popular formats for structured data in software development. JSON dominates API responses; YAML dominates configuration files. Understanding their trade-offs helps you pick the right one — and convert between them when you need to.
JSON and YAML both represent structured data but differ in syntax, readability, and use cases. Compare them side by side to decide which format suits your configuration files and APIs.
JSON
Open JSON →JSON (JavaScript Object Notation) expresses structured data using braces, brackets, colons, and commas. It is a strict subset of JavaScript object literal syntax and can be parsed by virtually every programming language with no dependencies.
Use cases
- REST and GraphQL API request and response bodies
- Browser localStorage and sessionStorage values
- package.json, tsconfig.json, and other JavaScript ecosystem config files
- NoSQL document databases such as MongoDB and Firestore
Strengths
- Universally supported — every language has a built-in JSON parser
- Strict syntax makes parsing unambiguous and fast
- Native to JavaScript and directly usable in browser environments
Limitations
- No comment syntax — you cannot annotate values inline
- Verbose compared to YAML for deeply nested structures
- All strings must use double quotes; trailing commas are forbidden
YAML
Open YAML →YAML (YAML Ain't Markup Language) uses indentation and minimal punctuation to represent the same structures that JSON expresses with braces and commas. It is a superset of JSON, meaning every valid JSON document is also valid YAML.
Use cases
- CI/CD pipeline configuration (GitHub Actions, GitLab CI, CircleCI)
- Container orchestration (Kubernetes manifests, Docker Compose)
- Infrastructure as code (Ansible playbooks, Helm charts)
- Application configuration files where human editability matters
Strengths
- Supports comments — great for self-documenting configuration
- More readable than JSON for humans when deeply nested
- Supports multiline strings natively without escape sequences
Limitations
- Indentation-sensitive — a single space error can change the meaning
- Many implicit type coercions (e.g. 'yes', 'no', 'on', 'off' become booleans)
- Slower to parse and more complex to implement than JSON
Use JSON for API responses, data interchange between services, and any context where machines are the primary consumer. Use YAML for configuration files, deployment manifests, and any file that humans will read and edit frequently — especially when comments or multiline strings are needed. If you are building a new API, default to JSON. If you are writing a CI/CD pipeline or Kubernetes manifest, default to YAML.
Is YAML a superset of JSON?
Yes. The YAML 1.2 specification defines YAML as a superset of JSON, meaning every valid JSON document is also valid YAML. You can parse a JSON file with a YAML parser without any changes. The reverse is not true — YAML comments and indentation-based structure are not valid JSON.
Why does YAML convert 'yes' and 'no' to booleans?
YAML 1.1 (still used by many parsers) treats 'yes', 'no', 'on', 'off', 'true', and 'false' (case-insensitive) as boolean values. This catches people out with country codes like 'NO' (Norway) or toggle keys. Quoting the value ('yes' as a string) prevents the coercion. YAML 1.2 restricts booleans to only 'true' and 'false'.
Can I convert JSON to YAML without losing data?
Yes — converting JSON to YAML is lossless because YAML is a superset of JSON. Converting YAML to JSON may lose data if the YAML uses features that JSON does not support, most commonly comments and multiline string literals (which become single-line strings in JSON).
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