Find the break, keep the source.
Errors include a line and column whenever available. Go to error selects that location in the editor. An error can be detected after its actual cause: a missing quote may make a later comma appear wrong.
Trailing commas
{"ok":true,} is not valid JSON. Repair commas prepares a result without commas immediately before closing brackets or braces, while preserving string contents. It succeeds only if the repaired document validates. Apply preview is a separate action.
Strings and object keys
Keys and string values need double quotes. Single quotes, comments, undefined, NaN and Infinity are not part of JSON. The tool does not guess missing values or convert arbitrary JavaScript into JSON.
Incomplete input
A half-typed document can be invalid while you work. The formatter waits briefly between edits and never overwrites the source automatically. Close the missing string or bracket, and formatting resumes.