TOML (Tom's Obvious, Minimal Language) is a configuration file format designed to be easy for humans to read and unambiguous for machines to parse, using key = value pairs grouped into [section] tables. It was created by GitHub co-founder Tom Preston-Werner in 2013, with the spec maintained at toml.io.
TOML pairs look like assignment statements, and every value has an explicit, unambiguous type — string, integer, float, boolean, date/time, array, or table — with no implicit type coercion:
[package]
name = "example"
version = "1.2.0"
edition = "2021"
[dependencies]
serde = { version = "1.0", features = ["derive"] }
[[bin]]
name = "cli"
path = "src/main.rs"[package] and [dependencies] are tables (equivalent to nested JSON objects); [[bin]] with double brackets defines an array of tables — useful when a config needs a repeated block, like multiple binaries or build targets. Dates and times use ISO 8601 literals natively, without quotes, so they parse as real datetime values rather than strings.
"true" (quoted) and true (bare) are different types — a common source of config bugs when copy-pasting between formats.[section.subsection] header — TOML is best for flat-ish configs, not deep trees.null; omitting a key is the usual workaround, which changes how "unset" is distinguished from "empty."Cargo.toml, pyproject.toml) rather than .toml alone, which can make them easy to overlook when auditing a repo for config files.