| `entries` | Yes | A list of entries to add to an event. |
| `key` | Yes | The key of the new entry to be added. Some examples of keys include `my_key`, `myKey`, and `object/sub_Key`. |
| `value` | Yes | The value of the new entry to be added. You can use the following data types: strings, Booleans, numbers, null, nested objects, and arrays. |
| `overwrite_if_key_exists` | No | When set to `true`, the existing value is overwritten if `key` already exists in the event. The default value is `false`. |
And then you run the `add_entries` processor using the example pipeline, it adds a new entry, `{"newMessage": 3}`, to the existing event, `{"message": "hello"}`, so that the new event contains two entries in the final output: