Open JSON Formatter and Validator, paste the document and choose Validate only. Start by fixing syntax before changing formatting. Keep the original when it came from a configuration file, an API response or a signed payload.
Start at the error, then look backwards
An error location is where parsing failed. A missing comma can be reported at the next property, and an unclosed bracket can be reported at the end. Read the nearby value and its separator rather than changing the indicated character blindly.
For example, this array has a trailing comma:
{"name":"Sample","tags":["draft","review",],"active":true}
Remove the comma after "review":
{"name":"Sample","tags":["draft","review"],"active":true}
The corrected document has three top-level properties. Its values include a string, an array of two strings and a boolean. Validate again after each repair so a later edit does not conceal the first problem.
Check the common syntax differences
JSON requires double-quoted property names and strings. Comments, trailing commas and single-quoted strings are not part of its grammar. A document contains one top-level value; several objects on separate lines need a JSON Lines workflow rather than validation as one document.
Inside strings, escape quotation marks, backslashes and control characters correctly. The JSON value null differs from the string "null", just as true differs from "true". RFC 8259 defines JSON's grammar and discusses interoperability concerns.
Formatting can change more than whitespace
Format mode parses and writes the data again. Numeric spelling can change, for example 1.50 to 1.5, and escape sequences may be written as their actual characters. Minify uses the same parse-and-write process with optional whitespace removed.
Duplicate property names need a separate raw-text review. This parser keeps the last value and does not report duplicate names as a syntax failure. Once parsed, earlier duplicate values are unavailable to formatting or sorting.
JavaScript numbers also have precision limits. Every integer is exactly representable through 9,007,199,254,740,991, while some larger values round. Long IDs belong in quoted strings when their exact digits matter. A warning is a reason to inspect the original; it cannot recover digits already changed upstream.
Compare structure after syntax passes
Sorting object keys can reduce distracting order changes before a line comparison in Text Compare. Array order stays significant. A comparison after parsing cannot expose duplicate keys that parsing discarded.
Valid syntax does not establish that required fields exist, types are correct or an account ID is real. Check the consuming system's schema and rules. JSON to TypeScript can suggest types from a sample, but inferred types do not validate an API contract or describe cases missing from that sample.
Keep the right source format
Use YAML and JSON Converter for YAML rather than manually deleting indentation or comments until the parser accepts it. Conversion has its own rules, including supported types and comments that cannot survive in JSON.
This formatter accepts up to 10,000,000 characters. Its statistics describe the parsed document; they do not prove that it is safe to execute, suitable for an import or identical to the original bytes. Validate the result in the application that will use it before replacing a working configuration.