JSON Duplicate Keys
JSON allows duplicate keys in an object, but parsers typically keep only the last value. Duplicate keys often indicate a mistake.
Common causes
- Building objects in a loop and reusing the same key.
- Merging objects without checking for existing keys.
- Manual editing that accidentally duplicated a key.
How to fix
- Search for repeated key names in your object.
- Use a validator or script to detect duplicate keys.
- Restructure data so each key appears once; use arrays if you need multiple values.
FAQ
- What happens with duplicate keys in JSON?
- Most parsers use the last occurrence; earlier values are overwritten. Behavior can vary.
- Is duplicate key valid JSON?
- Yes, it is valid per the spec, but it is usually a logic error.
Fix it now
Try in validator (prefill this example)