Free TOML Validator Online
Validate TOML syntax instantly in your browser — no server, no signup.
Input TOML
Validation Result
What Is a TOML Validator?
You committed a bad Cargo.toml or pyproject.toml and broke the build — it happens more than it should. TOML (Tom's Obvious Minimal Language) is a config format used by Cargo (Rust), Poetry (Python), and many other tools. A validator checks whether your file is syntactically correct: valid key names, no duplicate keys, proper table syntax, and well-formed values. The TOML 1.0 specification defines all the rules. Paste your TOML here and get an instant pass/fail with line-level error detail — before it reaches your CI pipeline. For online linting tools, TOML lint is a well-known alternative. Everything here runs locally in your browser.
This tool runs entirely in your browser. Your TOML is parsed locally; nothing is sent to a server. Invalid syntax produces clear error messages with line and column information.
TOML Validation Examples
Valid TOML has proper quoting. Invalid TOML often has unclosed strings. Telecom-themed examples:
Example 1: Valid TOML
Example 2: Invalid TOML (unclosed string)
Use Sample above to load examples into the editor.
How to Use This Tool
Paste or Upload
Copy your TOML and paste it into the left editor, or click Upload to load a .toml file. Use Sample for example data.
Check the Result
The right panel shows "Valid TOML" or lists specific errors. Fix issues and re-validate. For formatting valid TOML, use the TOML Formatter.
Copy or Fix
Use Copy to copy the validation result. Fix errors in your source and validate again until it passes.
Where TOML Validation Helps
Before committing pyproject.toml (used by Poetry), Cargo.toml (used by Cargo), or other config files, validate them here to catch typos, wrong indentation, or duplicate keys. CI pipelines and deployment scripts often fail on invalid TOML; validating first saves debugging time. If you need to convert TOML to JSON or YAML, use TOML to JSON or TOML to YAML after validation.
Frequently Asked Questions
Is my data private?
Yes. Validation runs in your browser. No data is sent to any server.
What errors does it catch?
Syntax errors: invalid key names, wrong table syntax, duplicate keys, bad indentation, malformed strings or numbers. It does not validate against a schema or check semantic rules.
Can I validate TOML with comments?
Yes. TOML supports # comments. The validator accepts standard TOML including comments.
Validator vs Formatter?
The Validator checks syntax only. The TOML Formatter reformats valid TOML with consistent indentation. Use the validator first to ensure your file is valid.