TOML Validator
TOML Validator - a browser-based developer tools utility.
Browser tool
About TOML Validator
TOML is designed to be unambiguous, which means it is stricter than it first appears: tables must be declared before use, keys cannot be redefined, and strings have rules about which quotes escape what. This tells you which of those a file has broken, and where. Validating is free, runs online, and needs no account. The file is checked in your browser and is never uploaded.
How to use it
- Paste the file or open itCargo.toml, pyproject.toml, or any other.
- Read the reported positionTOML errors are usually precise, because the grammar leaves less room for a mistake to be valid-but-different than YAML does.
The rules people trip over
A table header cannot be repeated, and a key cannot be assigned twice — both are errors rather than last-one-wins. Arrays of tables use double brackets, which is easy to forget. Basic strings in double quotes process escape sequences; literal strings in single quotes do not, which is why Windows paths belong in single quotes.
What it does not do
- This validates syntax against the specification. Whether the keys match the schema your tool expects is separate, and a perfectly valid TOML file can still be rejected by Cargo or a linter for using a key it does not recognise.
- Dotted keys and nested tables can express the same structure two ways, and the validator accepts both. Which one your tool prefers is a convention rather than a rule.
- Dates and times are first-class types in TOML rather than strings. An almost-correct timestamp fails here even though it would pass unnoticed in JSON.
Questions people ask
- Why is my Windows path failing?
- A double-quoted string treats backslash as an escape character, so C:\Users becomes an invalid escape. Use a single-quoted literal string instead, where backslashes are just backslashes.
- Can I define the same table twice?
- No. Redefining a table or a key is an error in TOML rather than an override, which is deliberate — it makes a config file impossible to misread.
Questions about ToolsVerse itself — privacy, cost, what happens to your files — are answered in the frequently asked questions.
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