How to Find and Fix JSON Syntax Errors

Confirm the response is supposed to be JSON

If an API response begins with HTML, inspect its HTTP status, final URL and Content-Type before editing its body. A login page or gateway response must be fixed at the request or server boundary; deleting angle brackets does not turn it into the intended data.

For an actual JSON document, reproduce the failure on a copy. Record the engine message and use any position the tool provides as a starting point, not a guaranteed byte offset or independent encoding diagnosis.

Repair one syntax defect at a time

The first example below has a trailing comma. Remove that comma only after checking the intended object. Unquoted keys, single-quoted strings and comments are also outside standard JSON. Do not remove punctuation globally because it may belong inside a string.

A Windows path needs escaped backslashes inside a JSON string. After each repair, parse again and inspect the resulting value, rather than assuming a successful parse means the intended data survived.

Invalid: {"name":"Example",}
Valid:   {"name":"Example"}

JSON source: {"path":"C:\\Reports"}
Parsed path: C:\Reports

Check values after syntax succeeds

Compare the repaired source with the original and check the keys, records and types the consumer needs. Valid JSON can still violate a schema or business rule. Ordinary JavaScript parsing can round large numeric identifiers; preserve them as strings where the contract permits.

Test the corrected payload in the receiving application or its contract tests. Stop when syntax, required structure and representative values are correct; a formatter alone cannot verify access rights, account balances or another domain-specific fact.

References

Use the linked specifications and product documentation to check behavior in your own environment.