---
title: "Get Message Definition"
method: GET
path: "/MessageDefinition"
tags: ["Metadata"]
---

# Get Message Definition

`GET /MessageDefinition`

### Returns MessageDefinitions supported by the target endpoint

The Message Definition retrieval is required to inform a Sender on building the payload. A request is made using the Service Identifier and workflow type values, linking to the useContext and event elements, respectively, in the Message Definition resource, returning a list of FHIR resources. 

The order of workflow beyond this point is relatively flexible, the only stipulation being responses occurring after requests.

### Sender

The request for Message Definition is the next step for a Sender following the metadata acquisition. 
The sender must request the Message Definition for the Service Identifier obtained previously, along with the type of workflow type e.g. booking-request, servicerequest-request. The Message Definition will contain a list of FHIR resources which the sender must include when making a booking or referral. 

### Receiver

A receiver dictates what they need from a sender making a request and the MessageDefinition is the mechanism to support this. The Message Definition details what FHIR resources need to be included in the body (payload).
The receiver may support multiple services e.g. Out-of-Hours, Clinical Assessment Service under one organisation (on the same system) and consideration should be given to maintaining service identifiers and workflow type against Message Definitions.  It's advisable to make this a configurable option which providers can maintain themselves as new services come onboard.

## Query parameters

- `context` string, required

## Response `200`

Success

## Other responses

- `4XX` — Below are examples of potential HTTP status codes and their associated error codes, which could be returned in the event of a fault. Guidance on error handling within BaRS can be found [here](https://simplifier.net/guide/nhsbookingandreferralstandard/Home/Core/1.4.0/Error-Handling). | HTTP status | Error code | Description | | ----------- | -------------------------- | --------------------------------------------- | | 400 | SEND_BAD_REQUEST | The API was unable to process the request. | | 400 | REC_BAD_REQUEST | The Receiver has responded stating the message was malformed. | | 401 | SEND_UNAUTHORIZED | The API deemed you unauthorized to make this request. | | 401 | REC_UNAUTHORIZED | The receiver deemed you unauthorized to make request. | | 403 | SEND_FORBIDDEN | Missing or Expired Token. | | 404 | PROXY_NOT_FOUND | No related people exist for given NHS number. | | 404 | REC_NOT_FOUND | Patient record for given NHS number has been invalidated and not superseded by another NHS number. | | 405 | SEND_METHOD_NOT_ALLOWED | HTTP Verb is not correct for this scenario.| | 405 | REC_METHOD_NOT_ALLOWED | Receiver does not allow this.| | 405 | PROXY_METHOD_NOT_ALLOWED | Proxy does not allow this.| | 406 | SEND_NOT_ACCEPTABLE | Senders message had an incorrect content type defined for a response.| | 408 | REC_TIMEOUT | The downstream domain processing has not completed within the configured timeout period. | | 409 | SEND_CONFLICT | | | 409 | REC_CONFLICT | | | 409 | PROXY_CONFLICT | | | 422 | SEND_UNPROCESSABLE_ENTITY | Message was not malformed but deemed unprocessable. | | 422 | REC_UNPROCESSABLE_ENTITY | Message was not malformed but deemed unprocessable. | | 422 | PROXY_UNPROCESSABLE_ENTITY | Message was not malformed but deemed unprocessable. | | 429 | SEND_TOO_MANY_REQUESTS | The user has sent too many requests in a given amount of time| | 429 | REC_TOO_MANY_REQUESTS | The user has sent too many requests in a given amount of time|
- `5XX` — Below are examples of potential HTTP status codes and their associated error codes, which could be returned in the event of a fault. Guidance on error handling within BaRS can be found [here](https://simplifier.net/guide/nhsbookingandreferralstandard/Home/Core/1.4.0/Error-Handling). | HTTP status | Error code | Description | | ----------- | -------------------------- | --------------------------------------------- | | 500 | REC_SERVER_ERROR | The receiver server has encountered an Error processing the request. | | 500 | PROXY_SERVER_ERROR | Proxy Error. | | 501 | SEND_NOT_IMPLEMENTED | The Request was not recognized. | | 501 | REC_NOT_IMPLEMENTED | The Receiver did not recognize the request. | | 501 | PROXY_NOT_IMPLEMENTED | The Proxy did not recognize the request. | | 503 | REC_UNAVAILABLE | The Receiver was unavailable to service the request.| | 503 | PROXY_UNAVAILABLE | The Proxy was unavailable to service the request. |

---

[API](https://skmtc.net/nhs/apis/booking-and-referral-fhir-api.md) · [All operations](https://skmtc.net/nhs/apis/booking-and-referral-fhir-api/llms.txt) · [OpenAPI document](https://skmtc-service-staging.skmtc.workers.dev/v1/apis/nhs/booking-and-referral-fhir-api/versions/5ebb9de06e11/schema)