TOML Validator

About Structure Validator

Answers two questions at once: does this document parse, and is there anything structurally wrong with it. JSON, XML, YAML, TOML, TOON, INI, .env, .properties and HCL are each checked with a real parser, and the failure is reported with the line and column where it stopped.

Beyond parsing, XML gets structural checks a parser stops short of — duplicate id attributes, bare ampersands and unclosed tags — because a document can be well-formed and still carry the mistakes that break a consumer.

JSON gets the check that matters most for it: a key written twice inside the same object. JSON.parse keeps the last one and says nothing, so a document can be entirely valid and have quietly lost half of what was written in it. The same key in two *different* objects is ordinary and is not reported.

The result carries a grade out of a hundred, on the same scale the SEO and speed tools use. It is nothing but the list printed beneath it: a fault costs twenty-five, something worth looking at costs eight, and a note that only explains how something works costs nothing. A document cannot score well while showing faults.

Where it helps

• A document that does not parse is a result, with the line it gave up on, rather than an error.
• Finds duplicate JSON keys, which parse without complaint and silently discard data.
• Adds structural checks that a parser stays silent about, such as a duplicate id.
• Grades what it finds, so two documents can be compared without reading both lists.
• Counts nodes and depth, which is how you spot a document that will hit a parser limit.
• Local, so unreleased schemas and live payloads are never uploaded.

Limits

• Syntax and structure only — it does not validate against a JSON Schema, an XSD or a DTD. The Schema Validator is the tool for that.
• The grade prices the problems it knows how to look for. A hundred out of a hundred means nothing was found, not that nothing is wrong.
• Parsing stops at the first syntax error, so a badly broken file may need more than one pass.
• The structural checks are a useful subset, not a conformance suite.
• A document can be perfectly valid and still be wrong for its consumer.

Frequently asked questions

Is this a W3C or schema validator?

No. It checks that the document parses and applies a set of structural checks. Schema conformance needs the schema, which this tool does not take.

Why report an unclosed tag when the document parsed?

The unclosed-tag check reads the source text rather than the parsed tree, so it catches a document that only survived because something further down closed the tag by accident.

What counts as a warning rather than an error?

Errors are things that will break a consumer, such as a duplicate id or a bare ampersand. Warnings are risks, such as a trailing comma in JSON or a tab-indented YAML file.

It says valid, so why does my API reject the payload?

Then the problem is semantic — a missing field or a wrong type. This confirms the document is well-formed, not that it matches a contract.

Related tools

• Structure Repair — Fix broken JSON, YAML, XML, TOML, TOON, INI, .env, .properties and HCL, listing every repair
• Structure Formatter — Pretty-print JSON, XML, YAML, TOML, TOON or HCL with a chosen indent
• Tree Viewer — Explore JSON, XML, YAML, TOML, TOON or HCL as a collapsible tree
• Structure Compare — Diff two JSON, XML, YAML, TOML, TOON or HCL documents by path
• Structure Converter — Convert between JSON, XML, YAML, TOML, TOON, HCL and CSV
• String Escaper — Escape a JSON, XML, YAML, TOML or TOON document for embedding, or read one back

More Structured Formats tools

• Structure Converter — Convert between JSON, XML, YAML, TOML, TOON, HCL and CSV
• String Escaper — Escape a JSON, XML, YAML, TOML or TOON document for embedding, or read one back
• Structure Formatter — Pretty-print JSON, XML, YAML, TOML, TOON or HCL with a chosen indent
• Structure Validator — Check JSON, XML, YAML, TOML, TOON or HCL and report structural problems
• Tree Viewer — Explore JSON, XML, YAML, TOML, TOON or HCL as a collapsible tree
• Code Generator — Turn a JSON, YAML, XML or other document into TypeScript, Go, C#, Python, Rust and more
• Schema Generator — Write a JSON Schema, XSD, Avro schema or .proto from a document you already have
• Schema Validator — Check a document against a JSON Schema, .proto, Avro schema, XSD or RELAX NG
• Table Viewer — Show the records in a JSON, XML, YAML, TOML or TOON document as a table
• Structure Compare — Diff two JSON, XML, YAML, TOML, TOON or HCL documents by path
• Structure Repair — Fix broken JSON, YAML, XML, TOML, TOON, INI, .env, .properties and HCL, listing every repair
• Structure Minifier — Strip formatting from JSON, XML, YAML, TOML or TOON
• Path Finder — Select nodes with JSONPath or XPath
• Protobuf & Avro Decoder — Read protobuf wire bytes and Avro container files without their schema
• Expression Evaluator — Reduce a JSONPath or XPath match to a single answer