TOML Validate — Free Online Tool

A TOML validator checks whether a TOML document is syntactically correct, catching malformed table headers, invalid strings, broken arrays, and duplicate keys before they cause runtime errors or CI failures. SWEDevTools: Prism provides a free, browser-based TOML validator that processes everything locally—no configuration files are ever uploaded to a server—making it safe for private project configs, credentials files, and internal tooling settings.

Features

• Strict TOML spec compliance: Validates against the TOML specification to match real-world parser behavior in Rust, Go, Python, and other ecosystem tools.
• Clear error messages: Reports specific parse errors with context to help you quickly locate and fix issues in complex configuration files.
• Works offline as a PWA: Install SWEDevTools: Prism and validate TOML files without an internet connection—essential for air-gapped or restricted environments.
• No signup required: Validate TOML instantly with zero account creation, no email verification, and no usage limits.
• Local-first privacy: All validation happens in your browser. No configuration data is sent to any server, keeping sensitive settings private.
• Pipeline chaining support: Chain validated TOML into format converters (TOML-to-JSON, TOML-to-YAML) or formatters in a single workflow.

Frequently Asked Questions

Is the TOML validator free?

Yes, the SWEDevTools: Prism TOML validator is completely free with no signup, no ads, and no usage limits.

Does the TOML validator work offline?

Yes. SWEDevTools: Prism is a PWA that works without an internet connection once installed on your device.

Is my data safe when validating TOML?

Yes. All validation happens locally in your browser. No TOML content is ever uploaded to a server, making it safe for private configs, credentials, and internal settings.

Is TOML the same as INI?

They share similarities, but TOML has a formal specification with typed values (strings, integers, floats, booleans, dates), arrays, and nested tables—making it more predictable and unambiguous than INI variants.

Are duplicate keys allowed in TOML?

No. The TOML specification prohibits duplicate keys within the same table. Duplicate keys cause parse errors or undefined behavior depending on the parser.

Why did my table header fail parsing?

Table headers must use square brackets and valid key names, e.g., [server]. Unterminated brackets, invalid characters, or missing closing brackets cause parse failures.

How do multiline strings work in TOML?

TOML supports multiline basic strings (triple double quotes) and multiline literal strings (triple single quotes). Be careful with escape sequences—basic strings process them, literal strings do not.

Does this validate application-specific rules?

No. The validator checks TOML syntax and structure only. Whether your keys and values are correct for your specific application (like Cargo.toml or pyproject.toml) requires application-level validation.

Why do date/time values fail validation?

TOML date/time formats are strict and must follow RFC 3339. Ensure proper separators and timezone suffixes, e.g., 2026-04-13T12:00:00Z.

How is this different from validating in my IDE?

IDE TOML support varies by editor and plugin quality. SWEDevTools: Prism provides consistent, spec-compliant validation in any browser, works offline, and integrates with pipeline workflows for format conversion.

Is Prism a good alternative to online TOML validators?

Yes. SWEDevTools: Prism validates TOML entirely in your browser with no server uploads, works offline as a PWA, requires no signup, and lets you chain validated TOML into format converters in a pipeline. Most online validators upload your configuration data to their servers.

What happened to smalldev.tools?

smalldev.tools is no longer available. Prism by SWEDevTools offers the same developer tools and more, with offline support, pipeline chaining, and completely free usage — no signup required.