An API client makes an HTTP request to an API gateway with an Accept header...

When an API client makes an HTTP request to an API gateway with an Accept header containing the value "application/json", the valid HTTP response payload should be in JSON format. The correct JSON format for indicating a healthy status is {"status": "healthy"}. This format uses a JSON object with a key-value pair where the key is "status" and the value is "healthy".

Other options provided are not valid JSON responses:

<status>healthy</status> is XML format.

status('healthy') and status: healthy are not valid JSON syntax.

References

HTTP Content Negotiation and Accept Headers

JSON Formatting and Syntax Rules