Fix JSON duplicate keys
JSON allows duplicate keys, but most parsers use only the last value. Duplicate keys can cause bugs and unexpected behavior.
The JSON specification allows duplicate keys, but behavior is undefined: most parsers keep the **last** value, which makes silent data loss easy.
Duplicates often come from merging configs, generated JSON, or hand-edited files.
Common causes
- Same key repeated in one object (`{"a":1,"a":2}`).
- Merge tools concatenating objects without deduplicating keys.
- Copy-paste leaving two versions of a field next to each other.
How to fix
- Remove duplicate keys and keep a single canonical value per key.
- Use a schema (JSON Schema) or linter in CI to reject duplicates if your stack supports it.
- Validate with the online JSON validator and inspect merged outputs in code reviews.
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