YAML vs TOML
Both formats were designed for human-edited configuration files and support comments with #.
YAML uses indentation to express arbitrarily deep trees; TOML uses explicit [section] headers and mandatory quotes around strings to eliminate implicit-typing surprises.
Convert between JSON and both formats using JSON to YAML, YAML to JSON, and JSON to TOML.
| YAML | TOML | |
|---|---|---|
| Structure mechanism | Significant leading whitespace (spaces only; tabs are syntax errors) | Explicit [table], [table.subtable], and [[array_of_tables]] headers; indentation is ignored |
| String quoting | Optional for most strings, which causes unquoted values like NO, on, or 3.10 to be coerced to booleans or floats | Mandatory quotes ("..." or literal '...') for all strings; numbers, booleans, and RFC 3339 dates have unambiguous syntax |
| Deep nesting ergonomics | Compact for deeply nested trees (Kubernetes specs, OpenAPI definitions, CI workflows) | Verbose when nesting exceeds 3 levels, since each level repeats dotted table headers or uses inline tables |
| Specification complexity | Large specification (YAML 1.1 vs 1.2 differences, anchors, aliases, custom tags) | Minimal specification (TOML v1.0.0) designed to map cleanly to a hash table |
| Standard ecosystems | Kubernetes, Docker Compose, GitHub Actions, Ansible, Helm, OpenAPI | Rust (Cargo.toml), Python packaging (pyproject.toml), Go/Hugo, Netlify (netlify.toml), Cloudflare Wrangler |
Which one should you pick?
Pick TOML for application and package configuration where settings are mostly 1 to 2 levels deep (build flags, dependency tables, environment overrides). Because TOML requires quotes on strings and ignores indentation, copy-pasting lines never silently corrupts the tree structure or turns a version string like 3.10 into the number 3.1.
Pick YAML when authoring deeply nested declarative graphs such as container orchestration manifests, CI/CD pipelines, or API specifications where repeating dotted section headers for every nested block would be noisy. Validate your indentation with YAML Viewer & Validator.
