YAMLとTOMLはどちらも人間が読めるconfig形式ですが、用途が異なります。5つの重要な違い：
[section]ヘッダーを使う。yes/noを暗黙的にbooleanに変換する。Configuration files define how your software behaves in every environment. YAML and TOML have become the dominant formats for modern developer tooling: Kubernetes uses YAML, Rust's Cargo uses TOML, and Python packaging has adopted TOML in pyproject.toml. This guide covers what you need to know about both formats, their common pitfalls, and how to move data between them.
YAML (YAML Ain't Markup Language) uses indentation to represent hierarchy — there are no braces or brackets. This makes it clean to read but notoriously sensitive to whitespace errors.
Indentation rules: YAML uses spaces only — never tabs. The number of spaces must be consistent within a document (2 or 4 spaces per level are standard). A single tab character anywhere in a YAML file causes a parse error.
Key-value pairs: Written as key: value with a mandatory space after the colon. Missing the space (key:value) is a common error.
Strings: Most strings don't need quotes. You need quotes when the value contains special characters or could be misinterpreted as a boolean. YAML 1.1 treats yes, no, true, false, on, off as booleans.
Multi-document YAML: Use --- to separate multiple documents in a single file — common in Kubernetes manifests that define multiple resources.
Tab characters — The most common and hardest to spot. Configure your editor to show whitespace characters and enforce spaces-only for YAML files.
Inconsistent indentation — Mixing 2-space and 4-space indentation in the same file causes silent structural errors. Use our YAML Formatter to normalise indentation in one click.
Implicit type coercion — YAML 1.1 treats yes/no/on/off as booleans and bare numbers as integers or floats. A port value of 0800 gets parsed as octal 512. Always quote ambiguous values.
Anchor and alias errors — YAML anchors (&name) and aliases (*name) are powerful but confusing. Our YAML to JSON Converter resolves anchors and shows the fully expanded result.
TOML (Tom's Obvious Minimal Language) was designed specifically for configuration files that humans edit directly. Unlike YAML, TOML is unambiguous — there is no indentation to miscount and no implicit type coercion.
Key sections: TOML uses [section] headers instead of indentation. A Cargo.toml file has sections like [package], [dependencies], and [dev-dependencies].
Array of tables: The [[table]] syntax creates an array of objects — used for things like multiple binary targets in Cargo.toml.
Types: TOML is strongly typed. It distinguishes integers, floats, booleans, strings, datetime, arrays, and inline tables. There is no implicit coercion — port = 8080 is always an integer.
Comments: Unlike JSON, TOML supports comments with #. This makes it ideal for configuration files where you want to explain each setting inline.
Use YAML when the tooling requires it (Kubernetes, Helm, Ansible, most CI/CD systems), when you need comments and anchors, or when the config is primarily written and read by machines.
Use TOML when humans edit the file directly and correctness matters more than compactness. Rust's Cargo.toml, Python's pyproject.toml, and Hugo's config.toml are canonical examples.
Use JSON when the config is consumed by JavaScript/Node.js code (package.json, tsconfig.json), or when you need the simplest possible format with maximum parser support.
Converting between these formats is straightforward: our JSON to YAML, JSON to TOML, YAML to JSON, and TOML to JSON converters handle the translation in your browser.
The most common cause is tab vs space indentation. Some editors insert tabs silently. Run your YAML through our YAML Formatter to normalise whitespace before committing.
Yes. YAML supports comments with #. Anything from # to the end of the line is ignored — one of YAML's main advantages over JSON for configuration files.
TOML v1.0 (released 2021) clarified edge cases around multiline strings, Unicode key names, and datetime formats. Most modern tools (Cargo 1.54+, Python's tomllib) use v1.0. Our formatter is v1.0 compliant.
Use our YAML to JSON Converter. Paste your manifest and click Convert. The output is valid JSON that kubectl and most Kubernetes clients accept.
The Python packaging community chose TOML because it supports comments (unlike JSON), is unambiguous (unlike YAML's implicit types), and is human-friendly. PEP 518 (2016) specified TOML for this purpose.