TOML is an INI-like format built for config files: explicit [table] headers, quoted strings, real date types and no meaningful indentation. YAML relies on indentation, guesses types from bare values and adds anchors and multiple documents. For shallow settings TOML is harder to break; for deep nesting YAML reads better.
| TOML 1.0 | YAML 1.2 | JSON | |
|---|---|---|---|
| Nesting | [table] and [a.b] headers | Indentation | Braces |
| Comments | # to end of line | # to end of line | None |
| Strings | Always quoted | Quotes optional | Always double-quoted |
| Dates and times | Built-in types | Not in the 1.2 core schema | Strings only |
| Case-sensitive | Yes | Yes | Yes |
| Media type | application/toml | application/yaml | application/json |
Updated
Most of the time you do not get to choose: Python packaging reads pyproject.toml, Rust reads Cargo.toml, and GitHub Actions and Docker Compose read YAML. When you do choose, seeing one config in all three formats makes the trade-offs obvious. Pick a sample below and compare.
Pick a sample. All three versions hold exactly the same data, so you can compare how each format spells it out.
# Shop settings
title = "Harbour Bakery"
debug = false
opens = 07:30:00
[database]
host = "db.internal"
port = 5432
[email]
from = "[email protected]"
retries = 3# Shop settings
title: Harbour Bakery
debug: false
opens: "07:30:00"
database:
host: db.internal
port: 5432
email:
from: [email protected]
retries: 3{
"title": "Harbour Bakery",
"debug": false,
"opens": "07:30:00",
"database": { "host": "db.internal", "port": 5432 },
"email": { "from": "[email protected]", "retries": 3 }
}In the app settings sample, TOML stores opens as a real local time, while the YAML and JSON versions keep it as a string.
| File | Format | Read by |
|---|---|---|
| pyproject.toml | TOML | Python build tools and packaging |
| Cargo.toml | TOML | Cargo, the Rust package manager |
| .github/workflows/*.yml | YAML | GitHub Actions |
| compose.yaml | YAML | Docker Compose |
| package.json | JSON | npm and other Node package managers |
| Markdown front matter | YAML (TOML with +++ in Hugo) | Static site generators |
Dotted keys and inline tables avoid extra headers for small groups, and dates are typed values, not strings.
site.name = "Harbour Bakery"
site.url = "https://harbour.example"
owner = { name = "Ana", email = "[email protected]" }
launched = 2026-11-02
updated = 2026-11-02T09:15:00Z
notes = """
Closed on public holidays.
Orders after 4pm ship next day."""Python projects describe themselves in pyproject.toml and Rust crates in Cargo.toml, so TOML is the norm in those ecosystems. Hugo also accepts TOML front matter between +++ lines.
CI pipelines, container setups and deployment manifests lean on YAML: GitHub Actions workflows and Docker Compose files are both YAML, and the extension you choose is mostly about consistency.
TOML's goal, in its own spec, is to map unambiguously to a hash table. That means no guessing: text needs quotes, booleans are only true and false, and every table is named in a header.
The price is repetition in nested data. Three levels deep, a TOML file repeats the table path in every header, while YAML just indents.
Neither wins everywhere. TOML's explicit headers and mandatory quotes make small and medium config files hard to misread. YAML handles deep nesting and long lists with less noise, at the price of whitespace-sensitive syntax and implicit typing.
The Python packaging guides define pyproject.toml with three tables: [build-system] for the build backend, [project] for metadata such as name, version and dependencies, and [tool] for settings of individual tools like linters.
Not everything. TOML has no anchors or aliases, no multiple documents per file and no null, since every key must be given a value. For configuration that rarely matters, but YAML data that leans on those features will not convert one to one.
Both use YAML. GitHub Actions workflows live in .github/workflows with a .yml or .yaml extension, and Compose looks for compose.yaml by default, still accepting docker-compose.yaml for older projects.
Yes. Three double quotes start a multi-line basic string that allows escapes, and three single quotes start a multi-line literal string that keeps its content exactly as written.
Related: YAML vs JSON, YAML comments, YAML to JSON converter, JSON formatter, pnpm vs npm.
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