How to diagnose and repair invalid JSON

Step-by-step approach

Paste or load JSON into the syntax validator to see the parser error.
Look for trailing commas, unquoted object keys, single-quoted strings and missing brackets.
Change the original text in a local editor, then validate again.
Use the formatter only after parsing succeeds; formatting cannot reconstruct missing content.
Export the corrected valid JSON as a new file.

Try the matching tool

Open JSON Validator to work on a local copy. Review the result before importing it elsewhere.

What this does not solve

Browser tools can validate known structures and transform available data, but cannot restore deleted or corrupted bytes, infer unknown business facts, or guarantee that a target system will import every field as intended.