About TOML Validator

Validate TOML configuration syntax with error details. Part of the DevTools Surf developer suite. Browse more tools in the Data / SQL collection.

Use Cases

• Validate Cargo.toml (Rust) or pyproject.toml (Python) before committing to avoid CI failures.
• Check TOML configuration files for Hugo static site generator or other tools that use TOML natively.
• Verify TOML syntax when migrating configuration from JSON or YAML.
• Detect common TOML mistakes (duplicate keys, invalid datetime formats) before application deployment.

Tips

• TOML is whitespace-sensitive in table arrays: [[array-of-tables]] requires a blank line before each entry in most renderers — inconsistent spacing causes parse errors that are hard to locate.
• Test edge cases: TOML datetimes (RFC 3339 format) are strict about timezone format — '2024-01-15T10:00:00Z' is valid; '2024-01-15 10:00:00' may not be accepted by all parsers.
• Use toml.decode() in your language runtime to validate locally before deploying — configuration syntax errors are the most common cause of failed application startups.

Fun Facts

• TOML (Tom's Obvious, Minimal Language) was created by Tom Preston-Werner (co-founder of GitHub and creator of Semantic Versioning) and first released in 2013.
• Cargo, Rust's package manager, uses TOML for its Cargo.toml manifest files — making TOML one of the most widely read configuration formats in the systems programming world.
• The Python Package Index (PyPI) adopted pyproject.toml as the standard project configuration file in PEP 518 (2016) and PEP 621 (2021), displacing the older setup.cfg and setup.py formats.

FAQ

TOML vs. YAML vs. JSON for configuration — which should I use?

TOML: best for simple hierarchical configs (Cargo, pyproject). YAML: best for complex structured configs (Kubernetes, GitHub Actions) but error-prone due to indentation sensitivity. JSON: best for APIs and data serialization, not human-authored config.

Can TOML have comments?

Yes — TOML supports comments with # (hash). This is a major advantage over JSON for configuration files, where comments are needed to explain non-obvious settings.