TOML Content

What is TOML Validator?

TOML (Tom's Obvious Minimal Language) is a configuration file format designed to be easy to read and write while mapping unambiguously to a hash table. It's used by Rust's Cargo (Cargo.toml), Python's pip and build tools (pyproject.toml), Hugo static site generator, and many other modern CLI tools. TOML aims to be more readable than JSON for configuration while being simpler and more strictly defined than YAML. This validator checks your TOML files for syntax errors like unclosed strings, duplicate keys, invalid values, and malformed sections — catching issues before they cause runtime failures in your application.

How to Use

Paste your TOML content in the text area, or click 'Load Sample' to see a well-formed example with sections, key-value pairs, and various data types.
Click 'Validate' to check for syntax errors — the validator scans for unclosed strings, duplicate keys, invalid values, and structural issues.
Review any errors with line numbers in the results panel below the input area.
Fix each error in your TOML file and re-validate until all issues are resolved.

Why Use This Tool?

Catch TOML syntax errors before deploying config files that could crash your application at startup

Validate Cargo.toml, pyproject.toml, and other TOML configs used by popular build tools and package managers

Check for duplicate keys and sections that cause unpredictable behavior in different TOML parsers

Verify string, number, boolean, and array values conform to the TOML specification

All validation runs in your browser — your configuration files never leave your device

Tips & Best Practices

TOML section headers use [section] syntax — they define separate namespaces for key-value pairs that follow them
Strings must be wrapped in double or single quotes — bare values like hello without quotes are invalid
Booleans are lowercase only: true or false — True, FALSE, or other variations are not valid TOML
Comments start with # and extend to the end of the line — they can appear on their own line or after a value
Use [[array]] for arrays of tables — each occurrence creates a new element in the array

Frequently Asked Questions

What is TOML?

TOML (Tom's Obvious Minimal Language) is a configuration file format designed to map unambiguously to a hash table. It's used by Rust's Cargo (Cargo.toml), Python's pip and build tools (pyproject.toml), Hugo config.toml, and many other projects. It aims to be more readable than JSON for configuration while being simpler than YAML.

TOML vs YAML vs JSON for config files?

TOML is best for simple, flat configuration with clear types and no surprising behavior. YAML is more powerful but has complex behavior (anchors, references, multiple document types) that can lead to subtle bugs. JSON is universal but lacks comments and is harder to write by hand. Choose TOML for straightforward configs, YAML for complex structures, and JSON for API/data exchange.

What files use TOML format?

Common TOML files include Cargo.toml (Rust), pyproject.toml (Python), Hugo config.toml, and many modern CLI tools. The .toml extension is standard. If you're working with Rust or Python projects, you'll encounter TOML regularly in build and packaging configurations.

Does this validator support all TOML features?

This validator covers the most common TOML features: sections, key-value pairs, strings, integers, floats, booleans, arrays, and inline tables. Some advanced features like multiline strings, dotted keys, and datetime values have limited support. For full TOML 1.0 compliance validation, consider using a dedicated parser library.

When should I NOT use TOML?

Avoid TOML when your configuration requires deeply nested structures (more than 3-4 levels), as TOML's table syntax becomes verbose and hard to read. Also avoid TOML for data interchange between services — JSON is more widely supported by APIs. For complex configurations with inheritance or templating, YAML with anchors may be more appropriate despite its quirks.

Is my TOML configuration data safe to paste here?

Yes. All validation happens entirely in your browser using JavaScript. Your TOML content is never sent to any server, stored, or transmitted. You can safely validate configuration files containing internal hostnames, database URLs, or other sensitive information.

Real-world Examples

Validating a pyproject.toml Before Building

A Python project's pyproject.toml has a duplicate key in the [project] section. The validator catches this before the build fails with a confusing error message.

Input

[project]
name = "myapp"
version = "1.0.0"
name = "my-app-v2"

Output

Line 4: Duplicate key "name" in section [project]

Catching an Unclosed String in Cargo.toml

A Rust project's Cargo.toml has an unclosed string value for the description field. The validator identifies the exact line number for quick fixing.