Why convert JSON to TOML?

TOML is increasingly the preferred format for project configuration files, especially in Rust and Python ecosystems. If you have existing JSON configs or API data that needs to be represented as TOML, this converter handles the transformation. TOML's explicit syntax and comment support make it more maintainable for configuration files than JSON. After converting, you can add comments to document each setting — something JSON fundamentally cannot do.

Common use cases for JSON to TOML conversion

Developers convert JSON to TOML when setting up pyproject.toml for Python projects with Poetry or PEP 621, creating Cargo.toml for Rust crates, or configuring tools like Netlify, Hugo, and Deno that use TOML. It is also useful when migrating project configs from JSON-based tooling to TOML-based alternatives, or when bootstrapping new projects from template data stored in JSON format.

JSON features that do not map to TOML

Most JSON structures convert cleanly, but a few features require special handling. TOML does not support null values — these are typically omitted from the output. TOML requires arrays to have homogeneous types, so a JSON array like [1, "two", true] cannot be directly represented. Deeply nested objects may produce verbose TOML with many [section.subsection] headers. Very large JSON files with many nesting levels may be more readable in JSON format than the equivalent TOML.

// JavaScript — JSON to TOML with @iarna/toml
import { stringify } from '@iarna/toml';
const data = { database: { host: 'localhost', port: 5432 } };
console.log(stringify(data));
// [database]\n// host = "localhost"\n// port = 5432

# Python — JSON to TOML (requires tomli-w)
import json, tomli_w
data = json.loads('{"database": {"host": "localhost", "port": 5432}}')
print(tomli_w.dumps(data))
# [database]\n# host = "localhost"\n# port = 5432

TOML structure and formatting

TOML organizes data into tables (equivalent to JSON objects) and values. Top-level keys appear first, followed by [table] sections for nested objects. Arrays of objects use [[double.brackets]] syntax. Keys use bare identifiers when possible and quoted strings for special characters. Values are strongly typed — TOML distinguishes between integers and floats, and supports date/time literals natively. The resulting format is clean, predictable, and designed to be edited by humans.

Adding TOML to your project workflow

After converting your JSON configuration to TOML, you can enhance it with inline comments explaining each setting, group related settings under meaningful table headers, and use TOML's native date types for version dates or expiry timestamps. Many editors provide TOML syntax highlighting and validation through plugins. The taplo language server powers TOML support in VS Code, Neovim, and other editors with auto-completion and error checking.