Quick Verdict
Use JSON when…
Use JSON for APIs, package configuration (package.json, tsconfig.json), data interchange between systems, and anywhere a machine will primarily read and write the file.
Use YAML when…
Use YAML for CI/CD pipelines (GitHub Actions, GitLab CI, CircleCI), Docker Compose, Kubernetes manifests, Ansible playbooks, and any config file humans frequently edit — the comment support alone is worth it.
JSON vs YAML: Feature Comparison
| Feature | JSON | YAML |
|---|---|---|
| Comments | Not supported | Supported (# comment) |
| Syntax strictness | Strict (no trailing commas, quoted keys) | Flexible (many equivalent forms) |
| Multi-line strings | Escaped \n sequences | Literal block (|) and folded (>) styles |
| Parse speed | Faster | Slower (more complex grammar) |
| Tooling support | Universal | Very broad |
| Superset relationship | JSON is a subset of YAML | YAML is a superset of JSON |
| Security (parsing risk) | Low (no executable nodes) | Higher (!! type tags can be dangerous) |
| Schema validation | JSON Schema (mature) | JSON Schema or YAML-specific schemas |
When JSON wins
- ✓Comments: Not supported
- ✓Syntax strictness: Strict (no trailing commas, quoted keys)
- ✓Multi-line strings: Escaped \n sequences
When YAML wins
- ✓Comments: Supported (# comment)
- ✓Syntax strictness: Flexible (many equivalent forms)
- ✓Multi-line strings: Literal block (|) and folded (>) styles
Frequently asked questions
Can I convert JSON to YAML?
Yes — any valid JSON file is valid YAML. Many editors (VS Code with YAML extension), online tools, and command-line tools (`yq`, Python's yaml library) convert between them. The reverse (YAML to JSON) loses comments and may need to flatten YAML-specific features.
Is YAML safe to parse from untrusted input?
Not with the default loader in most languages. Python's PyYAML `yaml.load()` without `Loader=yaml.SafeLoader` can execute arbitrary Python code via YAML type tags. Always use safe loading: `yaml.safe_load()` in Python. JSON has no equivalent risk.
Why does Kubernetes use YAML instead of JSON?
Kubernetes supports both YAML and JSON — `kubectl apply` accepts either. YAML is preferred in practice because it supports comments (for explaining what a manifest does), is more readable for multi-line values, and has less punctuation-heavy syntax that's easier to diff and review. Under the hood, Kubernetes converts YAML to JSON internally.
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