# Problem Detail

The [`application/problem+json`](https://tools.ietf.org/html/rfc7807) (Problem Detail) **MUST** be used to communicate details about an error.

Problem Detail is intended for use with the HTTP status codes 4xx and 5xx. Problem Detail **MUST NOT** be used with 2xx status code responses.

At the minimum, any Problem Detail response **MUST** have the `title` and `detail` fields. `title` value **SHOULD NOT** change from occurrence to occurence of the problem, except for purposes of localization (e.g., using proactive content negotiation) [read more](https://tools.ietf.org/html/rfc7807#section-3.1)

### Example

```javascript
{
  "title": "Authentication required",
  "detail": "Missing authentication credentials for the Greeting resource."
}
```

> NOTE: `title` and `detail` fields **SHOULD NOT** be parsed to determine the nature of the error. Instead `type` **MUST** be used.

## Optional Fields

It **SHOULD** have the `type` field with the identifier of the error, besides it **MAY** have the `instance` field with the URI of the resource in question. If the Problem Detail response has the `status` field it **MUST** have the same value as HTTP Status code from of the response.

```javascript
{
  "type": "https://adidas-group.com/problems/scv/unauthorized",
  "title": "Authentication required",
  "detail": "Missing authentication credentials for the Greeting resource.",
  "instance": "/greeting",
  "status": 401
}
```

> NOTE: The `type` field is an identifier, and as such it **MAY** be used to denote additional error codes. Keep in mind that the identifier should be a URI.

## Additional Fields

If needed, the Problem Detail **MAY** include additional fields, refer to [RFC7807](https://tools.ietf.org/html/rfc7807) for details.

## Validation Errors

When necessary, a Problem Detail response **MAY** include additional error details about the problems that have occurred.

These additional errors **MUST** be under the `errors` collection and **MUST** follow the Problem Detail structure.

### Example

Request:

```
POST /my-resource HTTP/1.1
Content-Type: application/json

{
  "age": -32,
  "color": "cyan"
}
```

Response:

```
HTTP/1.1 400 Bad Request
Content-Type: application/problem+json
Content-Language: en

{
  "type": "https://example.net/validation_error",
  "title": "Your request parameters didn't validate.",
  "instance": "/my-resource",
  "status": 400,

  "errors": [
    {
      "type": "https://example.net/invalid_params",
      "instance": "/age",
      "title": "Invalid Parameter",
      "detail": "age must be a positive integer"
    },
    {
      "type": "https://example.net/invalid_params",
      "instance": "/color",
      "title": "Invalid Parameter",
      "detail": "color must be 'green', 'red' or 'blue'"
    }
  ]
}
```

## Problem Detail and Content Negotiation

### Example

A request is made to retrieve a resource representation:

```
GET /greeting HTTP/1.1
Accept: application/hal+json
```

However, in order to make this request, the client needs to be authorized. Since the request is made without the authorization credentials the **401 Unauthorized** response is returned together with details using the `application/problem+json` media type:

```
HTTP/1.1 401 Unauthorized
Content-Type: application/problem+json
Content-Language: en

{
  "type": "https://adidas-group.com/problems/scv/unauthorized",
  "title": "Authentication required",
  "detail": "Missing authentication credentials for the Greeting resource.",
  "instance": "/greeting",
  "status": 401
}
```

## No Stack Traces or Server Logs

> *Problem details are not a debugging tool for the underlying implementation; rather, they are a way to expose greater detail about the HTTP interface itself.*
>
> *–* [*RFC7807*](https://tools.ietf.org/html/rfc7807)

A Problem Detail response **MUST NOT** contain a program stack trace or server log for debugging purposes. Instead, provide a `logref` field with reference to the particular server log.

## Working with Problem Detail

An API description **MAY** list all the error codes with which the API responds. The error responses **SHOULD** describre the error object model schema. It is **RECOMMENDED** to include examples of a possible error response. The error description and/or error example **MAY** list all the types of errors returned for a given error code.

## External resources

There are a whole plethora of libraries working with Problem Detail, for example, see [Zalando / Problem](https://github.com/zalando/problem) (Java).