TOML to INI Converter

Understanding TOML and INI

TOML (Tom's Obvious, Minimal Language) is a modern configuration format with explicit typing, nested tables, and arrays of tables. It was designed as an improvement over INI's limitations while keeping the same spirit of simplicity. TOML is used by Rust's Cargo, Python's pyproject.toml, and Hugo, among many other tools. For a full reference on TOML syntax and features, visit our TOML guide.

INI (Initialization) is one of the oldest configuration file formats, dating back to early Windows and MS-DOS. INI files use a simple structure of sections (denoted by square brackets) containing key-value pairs separated by equals signs. The format has no formal specification, which means different parsers handle edge cases differently. Despite its age, INI remains widely used in PHP configuration (php.ini), MySQL (my.cnf), Git (.gitconfig), systemd unit files, and countless Windows applications. For more details on INI conventions, see our INI guide.

Converting from TOML to INI is essentially a downgrade from a richer, typed format to a simpler, flat one. This trade-off is worthwhile when you need compatibility with legacy systems that only understand INI, or when you want the absolute simplest configuration format for a straightforward use case.

Why Convert TOML to INI?

While TOML is more capable than INI, there are legitimate reasons to convert modern TOML configurations to the simpler INI format:

• Supporting legacy Windows applications. Many older Windows desktop applications, games, and utilities read their settings from INI files. If you maintain configurations in TOML for your modern toolchain but need to deploy settings to these legacy apps, conversion is essential.
• Generating php.ini or MySQL my.cnf files. PHP and MySQL use INI-style configuration. If your infrastructure-as-code defines settings in TOML, converting to INI lets you deploy runtime configurations for these services without manual formatting.
• Simplifying configuration for embedded systems. Resource-constrained devices and embedded systems often use INI parsers because they are trivially simple to implement. Converting TOML to INI ensures compatibility with these minimal environments.
• Creating human-editable configuration for non-technical users. INI is arguably the simplest configuration format to understand. Converting TOML to INI can make configuration files more accessible to users who are not familiar with TOML's table and array syntax.

How the Conversion Works

TOML-to-INI is a cross-format conversion that uses JSON as an intermediate representation. Since INI is a simpler format than TOML, some information is necessarily simplified during the conversion:

1. Parse the TOML input using smol-toml, validating syntax and extracting typed values including tables, arrays, strings, numbers, booleans, and dates.
2. Convert to JSON intermediate. The TOML structure is represented as a JSON object tree, with tables as nested objects and arrays as JSON arrays.
3. Flatten nested structures. Since INI only supports one level of sections, nested TOML tables are flattened. A table like [database.pool] becomes the INI section [database.pool] with dot notation in the section name.
4. Serialize values as strings. All TOML values are converted to their string representations. Booleans become true/false, numbers keep their numeric form, and arrays are joined with commas.
5. Emit INI output with sections and key-value pairs formatted as standard INI.

The table below summarizes how TOML constructs are represented in INI:

Before and After Example

Below is a practical example showing a TOML application configuration and the simplified INI equivalent after conversion.

[general]
app_name = "MyApp"
version = "2.0.1"
debug = false

[server]
host = "localhost"
port = 3000
workers = 4

[database]
driver = "mysql"
host = "db.local"
port = 3306
name = "app_db"

[logging]
level = "info"
file = "/var/log/myapp.log"
max_size = 10

[general]
app_name=MyApp
version=2.0.1
debug=false

[server]
host=localhost
port=3000
workers=4

[database]
driver=mysql
host=db.local
port=3306
name=app_db

[logging]
level=info
file=/var/log/myapp.log
max_size=10

Notice how the TOML tables map directly to INI sections, and key-value pairs translate cleanly. The structure is simplified -- string quotes are removed, and all values become plain text. This INI file is immediately compatible with any INI parser, from Python's configparser to PHP's parse_ini_file.

Tips and Best Practices

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