✓ TOML Validator
Check TOML syntax with section, key-value, quote, and bracket checks. Detects duplicate keys, malformed values, and unbalanced brackets — all in your browser, no upload.
About the TOML Validator
This TOML validator runs entirely in your browser. Paste your TOML and click Validate to scan it for common syntax problems. The validator checks for well-formed section headers ([section] and [[array-of-tables]]), valid key names in key = value pairs, balanced quotes and brackets in values, duplicate keys within the same section, and basic value-type recognition (strings, integers, floats, booleans, dates, arrays, and inline tables).
What is TOML?
TOML (Tom's Obvious, Minimal Language) is a configuration file format designed for human readability. It uses a clear structure of sections, key-value pairs, and typed values. It is widely used in Rust's Cargo, Python's pyproject.toml, and many other projects as a modern alternative to INI or YAML.
What does it check?
- Section headers —
[name]and[[name]]must have balanced brackets and a valid dotted name. - Key-value pairs — keys must be bare (letters, digits, hyphens, underscores) or quoted; a
=and a value must follow. - String values — single- and double-quoted strings must be balanced; basic strings use double quotes.
- Array values — square brackets
[...]must be balanced. - Inline tables — curly braces
{...}must be balanced. - Duplicate keys — a key defined twice in the same section is flagged.
How to use the validator
- Paste your TOML into the input box.
- Click Validate.
- Read the result panel — valid TOML reports success; problems list each issue with its line number.
- Fix the issues in your editor and re-validate.
Frequently asked questions
Does it support all TOML 1.0 features? The validator covers the most common syntax rules. Advanced features such as multi-line basic strings, multi-line arrays, and date-time values are tolerated but not deeply parsed.
Why are duplicate keys an error? TOML forbids defining the same key more than once in the same table (section). This is a hard error in the spec because it makes the document ambiguous.
Is my TOML uploaded? No. All validation happens locally in your browser.