TOML Formatter & Validator
Format, validate, beautify, and convert TOML configurations online. Supports Cargo.toml, pyproject.toml, line/column diagnostics, 100% client-side.
| Feature | TOML | JSON | YAML |
|---|---|---|---|
| Human Readable | Excellent (Key-Value tables) | Moderate (Machine API) | Excellent (Indentation) |
| Comments Support | Supported (`#`) | Not Supported | Supported (`#`) |
| Native Dates & Times | First-class (`YYYY-MM-DD`) | Strings only | Supported |
| Primary Use Cases | Cargo.toml, pyproject.toml | REST APIs, config | Kubernetes, Docker |
Tables organize key-value pairs into explicit sections. Sub-tables use dot notation like [server.http].
Double brackets define lists of tables. Each [[item]] entry appends a new table element to the array.
What Is TOML?
TOML (Tom's Obvious, Minimal Language) is a configuration file format designed to be easy for humans to read and unambiguous to parse, using simple key = value pairs and [section] headers. It's the format used by Cargo.toml (Rust) and pyproject.toml (Python), among others.
How to Use the TOML Formatter & Validator
- Paste TOML to format or validate it.
- Review syntax errors with line and column information when the input is invalid.
- Convert to or from JSON to move configuration data between formats.
- Formatting normalizes spacing and structure while preserving the data.
Technical Notes
- TOML types are explicit at the syntax level — strings, integers, floats, booleans, dates, and arrays each have unambiguous literal forms, which is part of why it's popular for configuration files that need to be both human- and machine-friendly.
- Table headers like [dependencies] group the key-value pairs that follow until the next header, similar in spirit to a JSON object.
Frequently Asked Questions
How do TOML Dates and Times convert to JSON?+
TOML supports first-class Date, Time, and DateTime objects. When converting TOML to JSON, date-times serialize as ISO-8601 strings since JSON lacks a native date type.
Why can top-level JSON arrays fail in JSON → TOML?+
TOML requires a top-level table (key-value dictionary). Naked JSON arrays of primitive values are automatically wrapped under a top-level key ("items") to ensure valid TOML.