TOML

TOML (Tom’s Obvious Minimal Language) is a configuration file format built around one goal: be obvious to a human reading it while still mapping cleanly and unambiguously to a hash table. Created by Tom Preston-Werner, it reached a stable 1.0 specification and has become the default config format across a generation of developer tooling. It aims to be more readable than JSON for config and less ambiguous than YAML.

• Formal specification - A versioned, testable spec (1.0.0) defines exactly how a document parses, avoiding the surprises that plague looser formats.
• Unambiguous typing - Strings, integers, floats, booleans, dates, arrays, and tables all have clear, defined syntax.
• Human-first readability - Sections and key/value pairs read like an INI file, so config stays approachable.
• Deterministic mapping - Every valid document maps to a single hash table, which keeps tooling predictable.

In practice TOML rarely rides on the wire of an API itself; it shows up in the tooling around APIs — package manifests like Cargo.toml and pyproject.toml, linters, generators, and the config files that drive API pipelines and gateways. When I audit how teams govern their API workflows, the config format matters because it determines how reliably automation and agents can read and rewrite that configuration. TOML’s strict, well-specified parsing makes it a safer machine-editable substrate than ad-hoc formats, which is why it keeps spreading through the toolchains that build and deploy APIs.