How do I validate JSON online?

Paste your JSON into Specway's free JSON validator. The tool runs a strict parse and reports either 'Valid JSON' with byte count, max depth, and key count — or a precise error showing the line, column, and byte position where parsing failed. Everything runs in your browser; nothing uploads.

What's the difference between syntax validation and schema validation?

Syntax validation checks that JSON parses cleanly — quotes match, brackets balance, no trailing commas. Schema validation checks that a syntactically-valid document conforms to a contract (required fields, type constraints, enum values, format patterns). This tool does syntax. For schema validation against an OpenAPI spec or JSON Schema, use the JSON Schema Validator tool.

Why does my API say 'Invalid JSON' when the validator says it's valid?

The validator only checks JSON syntax. APIs typically check three more layers: (1) the body matches the expected Content-Type, (2) required fields exist, (3) field types and constraints match the schema. A syntactically-valid empty object {} can fail any of those. Check the API's error response — it usually names the offending field.

Does this tool detect duplicate keys?

JavaScript's native JSON.parse silently keeps the last duplicate, so the validator reports the document as valid. JSON spec says duplicate keys are technically allowed but discouraged. To detect them, use a strict parser with options to error on duplicates, or run the JSON Schema validator with additionalProperties:false plus an explicit key list.

Can I validate large JSON files?

Yes — the validator handles documents up to ~50 MB on modern hardware. For larger files, your browser may slow down because we keep the whole document in memory. Streaming validators like jq or Python's ijson handle gigabyte-scale files line-by-line without loading them whole.

What does "max depth" mean?

Max depth is the deepest level of nesting in your JSON. A flat object is depth 1; an object containing an array of objects is depth 3. Excessive depth (>20) often indicates a denormalized data structure that's hard to query and slow to serialize. APIs typically reject input deeper than ~32 levels to prevent stack-overflow attacks.

Is duplicate-key JSON safe?

It parses, but behavior is undefined across implementations. JavaScript keeps the last value; some Java parsers throw; some keep the first. If you control both ends, dedupe before sending. If you don't, treat duplicate keys as a bug — they create non-deterministic behavior across services.

How do I validate JSON online?

Paste your JSON into Specway's free JSON validator. The tool runs a strict parse and reports either 'Valid JSON' with byte count, max depth, and key count — or a precise error showing the line, column, and byte position where parsing failed. Everything runs in your browser; nothing uploads.

What's the difference between syntax validation and schema validation?

Syntax validation checks that JSON parses cleanly — quotes match, brackets balance, no trailing commas. Schema validation checks that a syntactically-valid document conforms to a contract (required fields, type constraints, enum values, format patterns). This tool does syntax. For schema validation against an OpenAPI spec or JSON Schema, use the JSON Schema Validator tool.

Why does my API say 'Invalid JSON' when the validator says it's valid?

The validator only checks JSON syntax. APIs typically check three more layers: (1) the body matches the expected Content-Type, (2) required fields exist, (3) field types and constraints match the schema. A syntactically-valid empty object {} can fail any of those. Check the API's error response — it usually names the offending field.

Does this tool detect duplicate keys?

JavaScript's native JSON.parse silently keeps the last duplicate, so the validator reports the document as valid. JSON spec says duplicate keys are technically allowed but discouraged. To detect them, use a strict parser with options to error on duplicates, or run the JSON Schema validator with additionalProperties:false plus an explicit key list.

Can I validate large JSON files?

Yes — the validator handles documents up to ~50 MB on modern hardware. For larger files, your browser may slow down because we keep the whole document in memory. Streaming validators like jq or Python's ijson handle gigabyte-scale files line-by-line without loading them whole.

What does "max depth" mean?

Max depth is the deepest level of nesting in your JSON. A flat object is depth 1; an object containing an array of objects is depth 3. Excessive depth (>20) often indicates a denormalized data structure that's hard to query and slow to serialize. APIs typically reject input deeper than ~32 levels to prevent stack-overflow attacks.

Is duplicate-key JSON safe?

It parses, but behavior is undefined across implementations. JavaScript keeps the last value; some Java parsers throw; some keep the first. If you control both ends, dedupe before sending. If you don't, treat duplicate keys as a bug — they create non-deterministic behavior across services.

Free Tool

JSON Validator (2026)

Validate JSON syntax instantly with line/column error pointers. See byte count, nesting depth, and key count for valid documents. Pure browser-side — your data never uploads.

Valid JSON · 128 bytes · depth 3 · 6 keys

JSON to validate

Result

Bytes:: 128
Max depth:: 3
Total keys:: 6

Two layers of JSON validation

Syntax validation (this tool) checks that the document parses — brackets balance, quotes match, no trailing commas. It tells you whether JSON.parse() would succeed.

Schema validation (the JSON Schema Validator tool) checks that a syntactically-valid document conforms to a contract — required fields exist, types match, enums are honored, regex patterns hold. APIs typically need both.

In practice, syntax errors are 80% of the bugs and are easy to find. Schema errors are 20% but harder to debug. Run syntax first; if that passes and the API still rejects, drop into schema validation.

Reading the error pointer

When parsing fails, the validator surfaces the native JS error — typically "Unexpected token X in JSON at position N". We translate that byte offset into line and column for you.

The position is where the parser noticed the problem, not always where it started. A missing quote earlier in the document might surface as an error 200 bytes later. Work backward from the pointer, scanning the structure level by level.

What the metrics mean

Bytes: total document size including whitespace. Good proxy for over-the-wire cost.
Max depth: deepest nesting level. Anything > 20 usually means the data model needs normalization. APIs commonly reject > 32 to prevent stack-attack DoS.
Total keys: count of object keys across the whole document. Helps gauge complexity at a glance and detect runaway nesting.

Why this matters in API workflows

Most "the API broke" tickets in API support queues are syntax errors in the request body. Devs copy a payload from somewhere, paste into curl, miss a quote, get a confusing 400. A 30-second validation pass on the body usually surfaces the issue.

If you publish API docs, every code sample needs the same pass. Specway validates examples against your OpenAPI spec at build time — if a doc example won't parse, the build fails. That's why we built this tool: same standard, same expectation.

Ship API docs that stay this clean

Specway turns your OpenAPI spec into a branded developer portal — auto-synced, searchable, with built-in playground and code samples in every language. Free tier available.

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Frequently asked questions