JSON Validator
Paste JSON and Prettify checks it as you type, pinpointing each syntax error with the line and column where it occurs so you can jump straight to it. Validation runs locally in your browser with no upload, so fix the problem in place and revalidate instantly.
What the validator checks for
A strict parser reports the exact position of the first problem and, where possible, every problem at once: missing or trailing commas, unterminated strings, invalid escape sequences, unquoted keys, and stray characters after the closing brace. Each message carries a line and column so there is no guessing.
Duplicate object keys are flagged as a warning rather than a hard error, because they parse but almost always signal a mistake. The raw view highlights the offending line inline so you can see the problem in context.
Fix errors without leaving the page
Switch to raw edit mode and correct the JSON directly, with the line-number gutter and highlighting keeping you oriented. Common non-standard input, such as trailing commas, comments, or single-quoted strings, can be cleaned up with the built-in repair action instead of hand-editing.
Every edit revalidates immediately, so you get a tight write-check-fix loop rather than a submit button and a wait.
Syntax is free; schema checks are Pro
Checking that a document is well-formed JSON, locating errors, and repairing them are all part of the free tier. Validating a document against a JSON Schema, which enforces required fields, types, and allowed values, is a separate Pro feature layered on top of the free syntax check.
Frequently asked questions
Is the JSON validator free to use?
Yes. Syntax validation, exact error locations, and the repair action are free with no account. Validating against a JSON Schema is the one validation feature reserved for Pro.
Is my document uploaded to check it?
No. The validator runs entirely in your browser, so the JSON you paste stays on your device and is never sent to a server to be checked.
Can it validate against a JSON Schema?
Schema validation, which checks required properties, types, and enums against a schema you supply, is a Pro feature. The free tier covers syntax and structural validity.
Will it catch duplicate keys?
Yes. Repeated keys in the same object are surfaced as a warning, since they are valid JSON syntactically but usually indicate a bug in whatever generated the file.
Are large integers reported as errors?
No. Numbers beyond JavaScript's safe integer range, such as Snowflake IDs, are preserved exactly and treated as valid rather than being flagged or silently rounded.