JSON vs TOML

When to choose JSON

Choose JSON when you need a universal interchange format that every tool and language supports. JSON is the right choice for API payloads, data storage, and any context where the file is primarily read by machines. Its strict syntax is also an advantage when you want unambiguous parsing.

When to choose TOML

Choose TOML for application configuration files, especially in Rust, Python, and Go ecosystems where TOML is the convention. TOML's flat section-based structure makes it easy to scan, comments let you document settings inline, and native date/time types eliminate parsing ambiguity.

What is JSON?

Douglas Crockford popularized JSON (JavaScript Object Notation) in the early 2000s as a lightweight data interchange format, and it was formalized as ECMA-404 in 2013 and RFC 8259 in 2017. Despite its name, JSON is language-independent and has become the dominant format for data exchange across the entire software industry. Every major web API — from REST services to GraphQL responses — uses JSON as its primary serialization format. The structure is built on two universal data constructs: ordered lists (arrays) and key-value maps (objects), with strings, numbers, booleans, and null as primitive values. This simplicity enables native parsing support in virtually every programming language. JSON's tree structure — with nested objects and arrays forming a hierarchical document — makes it ideal for representing complex data relationships while remaining human-readable.

Configuration files across the JavaScript ecosystem use JSON extensively: package.json for Node.js projects, tsconfig.json for TypeScript, and settings files for VS Code, ESLint, and Prettier. JSON Schema provides a vocabulary for annotating and validating JSON documents, enabling automated testing of API contracts. NoSQL databases like MongoDB, CouchDB, and Firebase store documents in JSON-like formats, and PostgreSQL includes native JSON and JSONB column types. Tools like jq enable command-line JSON processing, while JSON Patch (RFC 6902) and JSON Merge Patch (RFC 7396) define standardized approaches for describing modifications to JSON documents. The format's ubiquity means that JSON comparison is one of the most frequently performed diff operations in software development.

• Wikipedia
• JSON Specification (ECMA-404)
• RFC 8259 — JSON Standard
• MDN — JSON
• JSON.org

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What is TOML?

Tom Preston-Werner — co-founder of GitHub — created TOML (Tom's Obvious, Minimal Language) in 2013, frustrated by the ambiguities and complexity of existing configuration formats. TOML prioritizes being obvious to read, with a minimal syntax of key-value pairs organized into tables (sections) denoted by [square brackets]. The format has become the standard configuration language for several major ecosystems: Cargo.toml defines Rust project metadata and dependencies, pyproject.toml (PEP 518/PEP 621) is the modern Python project configuration standard, Hugo uses TOML for site configuration, and Deno uses it for configuration files. TOML supports strings, integers, floats, booleans, dates and times (RFC 3339), arrays, and tables (maps), with a clear distinction between inline and multi-line representations. The specification reached version 1.0 in January 2021, marking stability after eight years of refinement.

Unlike YAML, TOML avoids indentation-based scoping and implicit typing — every value's type is explicit from its syntax, eliminating the class of bugs where strings are accidentally parsed as numbers or booleans. Unlike JSON, TOML supports comments and is designed for human editing rather than machine interchange. The hierarchical table structure — where [table.subtable] headers define nested objects — provides a clean way to organize complex configurations without deep nesting. Parsers exist for every major language, and the specification includes a comprehensive test suite for verifying parser compliance. TOML files are naturally structured as a tree of tables and key-value pairs, making them suitable for structural comparison that understands the difference between section reorganization and actual value changes.

• Wikipedia
• TOML Specification
• TOML GitHub Repository

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