Online JSON Validator — Check Syntax with Line Numbers

Paste JSON and get instant syntax validation with clear error messages. Runs entirely in your browser — ideal before minifying, converting or committing API fixtures.

JSON to validate

Validation runs entirely in your browser. Nothing is uploaded to FastMinify.

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JSON validator — syntax checking playbook

Validate JSON before minifying, converting or committing fixtures. FastMinify reports precise line and column positions for syntax errors — nothing leaves your browser.

Developer notes

• Validation runs automatically after you pause typing (debounced) — no server round-trip. • Errors surface with line and column numbers so you can jump straight to the typo. • Structure stats (keys, objects, arrays, depth) help sanity-check large payloads. • This page focuses on validation only — use the JSON minifier when you need compression, or the formatter for prettify-only workflows.

When teams pick this route

• Gate CI fixtures or OpenAPI snippets before they land in repos. • Confirm exports from YAML/CSV/XML converters parse cleanly. • Debug truncated API responses or copy-paste accidents in support tickets. • Quick check before diffing two configs or exploring them in the tree viewer.

Worked examples

Valid API envelope

Sample input

{
  "status": "ok",
  "items": [
    {"id": 1, "label": "alpha"}
  ]
}

Validation result

✓ Valid JSON — stats show keys, depth and value types in the status bar.

Trailing comma caught

Sample input

{
  "enabled": true,
  "tags": ["prod",],
}

Validation result

✗ Invalid JSON — error at the trailing comma with line/column hint.

Navigate related JSON tools

Prettify valid payloads with the JSON formatter, compare revisions via JSON diff, or browse structure in the JSON tree viewer. Compress for APIs with our JSON minifier, or change serialization via JSON → YAML and JSON → CSV.