RFC 9457 defines a standardized format for communicating error details in HTTP API responses, known as "problem details."
- Supersedes RFC 7807,
- Core fields include 'type', 'title', 'detail' and 'instance'.
- Generally paired with 4xx/5xx HTTP status codes.
- Content types `application/problem+xml`, `application/problem+json`
Example:
```
{
"type": "
https://example.com/probs/invalid-input",
"title": "Invalid Input",
"status": 400,
"detail": "The provided 'age' value must be a positive integer.",
"instance": "/users/123",
"age": -5
}
```