TOML Configuration: A Developer's Guide
TOML Configuration: A Developer's Guide
TOML (Tom's Obvious Minimal Language) is an increasingly popular configuration format. It's used by Cargo (Rust), pyproject.toml (Python), Hugo, and many modern tools.
Why TOML?
TOML occupies a sweet spot between YAML and JSON:
Syntax
Key-Value Pairs
title = "My App"
port = 8080
debug = false
pi = 3.14159
Strings
basic = "Hello\nWorld" # Escape sequences processed
literal = 'C:\Users\name' # No escape processing
multiline = """
This spans
multiple lines
"""
Tables (Objects)
[database]
host = "localhost"
port = 5432
name = "mydb"
[database.pool]
min = 5
max = 20
Arrays
ports = [8080, 8081, 8082]
hosts = ["alpha", "beta"]
Array of Tables
[[servers]]
name = "alpha"
ip = "10.0.0.1"
[[servers]]
name = "beta"
ip = "10.0.0.2"
This produces: servers = [{name: "alpha", ip: "10.0.0.1"}, {name: "beta", ip: "10.0.0.2"}]
Dates and Times
created = 2026-01-15T09:30:00Z
date_only = 2026-01-15
time_only = 09:30:00
TOML vs YAML vs JSON
| Feature | TOML | YAML | JSON |
|---------|------|------|------|
| Comments | Yes | Yes | No |
| Date types | Native | No | No |
| Indent-sensitive | No | Yes | No |
| Nested depth | Flat preferred | Any | Any |
| Boolean gotchas | No | Yes (Norway) | No |
When to Use TOML
TOML works best for configuration files with flat or shallow structure. It gets awkward with deeply nested data — that's where YAML or JSON may be better.
Try It
Use our TOML ↔ JSON Converter to convert between formats and see how TOML tables map to JSON objects.
Conclusion
TOML is clean, unambiguous, and well-suited for configuration files. If your config is mostly flat key-value pairs with some grouping, TOML is an excellent choice.