YAML vs TOML
Pick YAML for ecosystems that already speak it — Kubernetes, CI pipelines, Ansible — and for deeply nested documents humans must read. Pick TOML when a file should be unambiguous, paste-safe and strictly typed: quoted strings, native dates, explicit structure. Both support comments, both are config languages, and converting between them is routine.
YAML vs TOML explained
YAML and TOML exist for the same reason: JSON makes miserable configuration — no comments, mandatory quotes on every key, braces to count. Given that shared starting point, the two made opposite bets. YAML bet on brevity through inference: quotes usually optional, nesting expressed by indentation, structure implied. TOML bet on explicitness: strings must be quoted, sections must be declared with [headers], and nothing is guessed. Neither bet is wrong; they optimise for different failure modes.
YAML's bet buys compact, deeply readable files — and an entire error class TOML does not have. Indentation mistakes silently reshape documents, and bare scalars are typed by inference, so a country code like NO becomes boolean false (the Norway problem). TOML's bet buys files that are longer at depth but nearly impossible to misread: the grammar is small, versioned semver-stable at 1.0 since 2021, and a value's type is always declared by its syntax.
This page compares the two where choices get made: syntax and structure, typing and the classic surprises, comments and anchors, and the ecosystems — Kubernetes and CI for YAML, Cargo and Python packaging for TOML — that usually decide for you first.
The fastest way to feel the typing difference is to convert the same file both ways — the YAML to JSON converter shows exactly what every bare scalar became, in your browser.
Curious what TOML's explicit style reduces to? The TOML to JSON converter runs the parse locally and labels nothing, because nothing needs inferring.
Two philosophies: inferred versus declared
The single deepest difference is where structure lives. In YAML, structure is whitespace: indentation levels define nesting, and tabs are forbidden outright. In TOML, structure is punctuation: a line like [database.pool] declares a table, and indentation is purely cosmetic. Everything else on this page — paste safety, verbosity at depth, error messages — follows from that one decision.
| Aspect | YAML 1.2 | TOML 1.0 |
|---|---|---|
| Structure | Indentation (spaces only; tabs forbidden) | [table] headers and dotted keys |
| Strings | Quotes usually optional | Always quoted — "..." or '...' |
| Typing | Inferred per parser; NO becomes false | Declared by syntax; nothing inferred |
| Datetimes | Timestamp type, parser-dependent | Native RFC 3339 date-times |
| Anchors | & anchors and * aliases | None — values repeat or are generated |
| Multi-document | Yes — --- separated streams | One document per file |
| Comments | # to end of line | # to end of line |
| Spec stability | 1.2 (2009), layered and intricate | 1.0 (2021), small and semver-stable |
Syntax: indentation versus table headers
Shallow config flatters both formats; deep nesting separates them. YAML keeps getting quieter as structure grows — two spaces and a dash — while TOML writes one header per level: [database.pool.limits], then [database.pool.limits.read]. At three levels TOML is merely verbose; at eight, YAML is the only sane hand-written choice. Arrays of tables invert the verdict: TOML's [[products]] blocks are crisp and greppable, while long YAML lists of maps are exactly where columns drift.
Paste safety follows directly. Dropping a block into YAML one column too far left or right either breaks parsing or — worse — silently changes what it means; the file still parses and nothing warns you. In TOML a pasted block carries its own [header], so it lands where its heading says regardless of the surrounding whitespace.
Types and the Norway problem
YAML infers scalar types, and inference has teeth: yes, no, on and off become booleans under the YAML 1.1 rules many parsers still ship, NO becomes false, and a version written 1.20 can arrive as the number 1.2. YAML 1.2 trimmed the rules but did not unify parsers, so the same file can type differently across tools. The defence is quoting anything that must stay a string.
TOML has no inference step to get wrong: quotes make a string, bare digits make an integer (underscores allowed for readability), and RFC 3339 timestamps are a first-class type — a genuine advantage over both JSON and YAML for config that carries dates. Multi-line strings exist in both: TOML's triple-quoted """ blocks and YAML's | and > scalars.
Ecosystems and when to pick which
Ecosystems have already carved the territory. YAML owns cloud-native and CI: Kubernetes manifests, GitHub Actions and GitLab CI, Ansible, docker-compose, OpenAPI descriptions. TOML owns packaging and tooling metadata: Rust's Cargo, Python's pyproject.toml, and a long list of CLI tools that want unambiguous, comment-friendly config. Choosing against an ecosystem means fighting its tooling forever, so this is rarely a free choice.
Where you do choose: pick YAML for deeply nested, human-reviewed documents, and TOML when values must be unambiguous, diffs exact and files edited by both humans and generators. The guidance reverses routinely — most repositories hold both — and the converters linked here bridge either direction locally.
Frequently asked questions
Is TOML replacing YAML?
No — the two have split the territory rather than fought over it. YAML is entrenched where cloud-native tooling mandates it: Kubernetes, GitHub Actions, Ansible, docker-compose. TOML is entrenched in packaging: Cargo.toml, pyproject.toml and most modern CLI tool configuration. New tools increasingly pick TOML for simple settings, but no serious migration away from YAML is happening at scale.
Does TOML have the Norway problem?
No. YAML infers types for bare scalars, so NO parses as boolean false and on or off become booleans too. TOML requires every string to be quoted, so "NO" is unambiguously a string and nothing is ever inferred. The YAML defence is the same discipline TOML mandates: quote any value that must remain text.
Do the YAML and TOML converters upload my config?
No. Parsing and emitting run inside your browser tab — there is no upload endpoint, and the site's Content-Security-Policy permits network requests only to itself. Open the DevTools Network panel while converting and you will see no outbound request; the files you paste stay in the tab.
Why does TOML get so verbose for nested config?
Every nesting level needs its own bracketed header: [database.pool.limits.read] declares three lines of scope before the first value. That verbosity is also the feature — sections are greppable, scope is unambiguous, and diffs show exactly what moved. If your config nests eight levels deep, YAML's indentation is genuinely the better fit.
Do YAML and TOML both support comments?
Yes — both use # to the end of the line, which is precisely why both displaced JSON for configuration. They differ in almost everything else: anchors and multi-document streams exist only in YAML, while TOML offers native RFC 3339 dates and a semver-stable 1.0 grammar that YAML has never matched.
Which format is safer to copy and paste?
TOML. A block pasted into YAML must land at exactly the right indentation column, or the document's meaning silently changes; even when it parses, nothing warns you. TOML blocks are delimited by their own [headers], so indentation is cosmetic and a pasted section means what its heading says wherever it lands.