TOOL GUIDES
How to Fix Invalid JSON and Preserve Large IDs
Check JSON syntax, find common formatting errors and preserve large numeric identifiers when formatting.
Know what validation checks
JSON validation checks whether the document follows JSON syntax. It does not confirm that an API accepts the fields or that the values are correct for your business. A document can be valid JSON and still contain a missing customer identifier or the wrong date. Use the API specification alongside the formatter. Before pasting logs, remove credentials, access tokens and personal information, especially if you later copy the output into a support message.
Check quotes and separators
JSON property names and string values require double quotes. Single quotes are not valid JSON string delimiters. Separate properties and array items with commas, but do not put a trailing comma before a closing bracket. Comments are also not part of standard JSON. If copied data begins with a variable assignment or includes a console prefix, remove that wrapper before validation. Do not delete punctuation randomly: identify the structure around the error first.
Handle strings and special characters
A quote inside a string needs escaping, and a literal line break cannot appear inside a JSON string. Use the JSON escape sequence for a newline instead. An escaped backslash is also different from a single backslash in a path. Values such as true, false and null must be lowercase and unquoted when you intend their JSON types. Quoted versions are strings. If the validator reports a position, examine the nearby text and the preceding property, where the actual mistake may have started.
Preserve identifiers and precision
Some identifiers are larger than JavaScript can represent exactly as numbers. GetFree4U checks syntax and formats the original tokens, preserving their written numeric digits instead of reserializing parsed numbers. For example, the ID 9007199254740993123 remains unchanged in formatted output. This does not make every downstream program safe: an application that parses it as a JavaScript number can still lose precision. When an API defines an identifier as a string, keep it quoted according to that specification.
Format, minify and review
Choose formatting when you want indentation that makes nested objects easier to inspect. Choose minification when you only need unnecessary whitespace removed. Both operations preserve the document content rather than correcting its meaning. Duplicate keys are retained, so review them yourself: different applications may interpret repeated property names differently. The tool accepts up to two million characters and processes the document in your browser. Copy or download the result, then run the actual API or application check separately. If validation fails, output is cleared so you do not accidentally reuse a previous result. Keep an untouched copy of the source until you have verified the corrected document.