YAML to TOML Converter

No. Both formats support `#` line comments, but comments are trivia attached to the source text, not to the data model. The converter parses YAML into mappings, sequences, and scalars, then re-serializes that structure as TOML — any `#` comments in the original YAML are discarded in the process and won't appear in the TOML output.

YAML lets you write a mapping or sequence inline, like `{host: localhost, port: 5432}` or `[web, production]`, as an alternative to multi-line block style. TOML has a direct equivalent — inline tables (`{ host = "localhost", port = 5432 }`) and inline arrays (`["web", "production"]`). Since flow and block YAML parse to the identical data structure, the converter treats them the same way regardless of which style the source file used.

Yes. TOML's spec doesn't require any particular key order for two documents to be considered equivalent, but the converter still emits keys in the order they appeared in the YAML source, since standard parsers (PyYAML, js-yaml, ruamel.yaml) retain document order by default — this keeps diffs against the original file predictable.

TOML restricts unquoted ("bare") keys to ASCII letters, digits, underscores, and dashes. A YAML key like `first name` (a space) or `api.version` (a literal dot, which TOML would otherwise read as nested-table notation) doesn't fit that grammar, so the converter wraps it in quotes instead — producing `"first name" = "Jane"` — which TOML's spec defines as an equally valid alternative to a bare key.

Yes, but the relationship is what you lose, not the data. YAML anchors (`&name`) mark a block for reuse, and aliases (`*name`) copy that content elsewhere in the same document — commonly used for shared defaults, like a `&defaults` anchor merged into several environment configs with `<<: *defaults`. TOML has no anchor, alias, or merge-key concept, so before emitting TOML the converter resolves every alias to its expanded, literal value first. The result is data-equivalent — every field has the same value — but the "single source of truth" is gone: if the anchor block changes, you'd previously update it once in YAML, whereas in TOML you now have several independent tables to edit by hand. Multi-document YAML files (multiple `---`-separated documents) hit the same wall for a different reason: a TOML file is exactly one document, so only one YAML document survives conversion.

Usually because a specific toolchain requires TOML and won't accept YAML as a substitute. Rust's Cargo reads `Cargo.toml`; Python's Poetry, Hatch, and PDM read `pyproject.toml`; Hugo accepts TOML front matter in content files; and any tool built on Rust's `toml` crate or Go's BurntSushi/toml library expects TOML specifically. Teams that already maintain infrastructure or CI configuration in YAML — Ansible playbooks, GitHub Actions workflows, Kubernetes manifests — sometimes need to lift specific values (service names, ports, version pins) out of those files and into a TOML-based project or package manifest without hand-retyping every field and re-checking quoting and types. Running the source YAML fragment through a converter is faster and less error-prone than manually transcribing nested keys into bracketed TOML tables, especially for larger config blocks with several levels of nesting.

YAML is the older format by over a decade: version 1.0 was published in 2004 by Clark Evans, Ingy döt Net, and Oren Ben-Kiki, and the current revision, YAML 1.2.2, was finalized in 2021 and defines YAML as a strict superset of JSON. TOML is newer and was created in 2013 by Tom Preston-Werner, a GitHub co-founder, specifically to be a minimal, unambiguous configuration format — an alternative to both YAML's complexity and INI's lack of standardization. Cargo, Rust's package manager, was an early and influential adopter, which helped establish TOML as the default choice for Rust and later Python packaging manifests. TOML reached its first stable release, v1.0.0, in 2021, the same year as YAML's latest revision, so both specs you're converting between today are their most current, stable versions.

No — despite looking similar in places, they were designed independently and TOML's syntax is closer to INI files (`[section]` headers, `key = value` lines) than to YAML's indentation-driven block style. TOML deliberately has no concept of flow versus block style, no anchors or aliases, no custom type tags, and no multi-document files — it aims for exactly one way to write any given structure, which is precisely what lets this converter map YAML's nested mappings into TOML tables deterministically. The relationship only runs one direction cleanly: any valid TOML document can be re-expressed in YAML with no loss, but the reverse isn't true, since YAML's feature set is a strict superset of what TOML's grammar is able to express.

Cleanly, because both formats treat them as native types rather than strings. YAML's core schema recognizes timestamp scalars like `2024-01-15` or `2024-01-15T10:30:00Z` and tags them as dates rather than text; TOML v1.0.0 defines four distinct date/time types — offset date-time, local date-time, local date, and local time — each with its own grammar. The converter maps a YAML timestamp to whichever of TOML's four types matches the components actually present: a bare `2024-01-15` becomes a TOML local date, while a timestamp with a `Z` or `+00:00` offset becomes an offset date-time. Both formats follow RFC 3339 formatting for these values, so no reformatting of the date string itself is needed — only the type classification changes on the TOML side.