Self Assessment Assist (MTD) - HMRC Developer Hub

Dates and amounts
Date	Amount
Version and status	Select version and status
Available in Sandbox	Yes
Sandbox base URL	https://test-api.service.hmrc.gov.uk
Available in Production	No

Overview

The HMRC Assist report is based on the customers’ National Insurance number (nino) and Calculation ID. The report contains a list of ‘Errors’, ‘Warnings’, and ‘Info’ for the given National Insurance number (nino) and Calculation ID.

This API allows developers to:

retrieve a HMRC Assist report for a given customer with a list of warnings and possible errors
securely generate a report that is sent to or displayed after it has been generated
allow the client to acknowledge the report

Send fraud prevention data

HMRC monitors transactions to help protect your customers' confidential data from criminals and fraudsters.

Warning You are required by law to submit header data for this API. This includes all associated APIs and endpoints.

Check the data you need to send. You can also use the Test API during initial development and as part of your quality assurance checks.

Versioning

When an API changes in a way that is backwards-incompatible, we increase the version number of the API. See our reference guide for more on versioning.

Errors

We use standard HTTP status codes to show whether an API request succeeded or not. They are usually in the range:

200 to 299 if it succeeded, including code 202 if it was accepted by an API that needs to wait for further action
400 to 499 if it failed because of a client error by your application
500 to 599 if it failed because of an error on our server

Errors specific to each API are shown in the Endpoints section, under Response. See our reference guide for more on errors.

Changelog

You can find the changelog in the self-assessement-assist-changelog GitHub wiki.

Support

Raise non-technical or platform-related issues with the Software Development Support Team (SDST).
Raise technical issues on the self-assessment-assist-changelog GitHub page.

Testing

You can use the sandbox environment to test this API. You can use the Create Test User API or it's frontend service to create test users.

It may not be possible to test all scenarios in the sandbox. You can test some scenarios by passing the Gov-Test-Scenario header. Documentation for each endpoint includes a Test data section, which explains the scenarios that you can simulate using the Gov-Test-Scenario header.

If you have a specific testing need that is not supported in the sandbox, contact our support team.

Some APIs may be marked [test only]. This means that they are not available for use in production and may change.

Endpoints

Self Assessment Assist

Here a developer can:

request a HMRC Assist report to be generated for a customer or their advisors
Allow the client to acknowledge the report

Self Assessment Assist resources

Produce a HMRC Self Assessment Assist Report

POST

This endpoint allows a developer to generate and return a HMRC Assist report for a tax calculation and taxpayer.

Authorisation

This endpoint is user-restricted and requires an Authorization header containing an OAuth 2.0 Bearer Token with the read:self-assessment-assist scope.

Path parameters

Path parameters table
Name	Description
nino string required	National Insurance number, in the format AA999999A. For example: `TC663795B`
calculationId string required	The unique identifier for the calculation. Must conform the regular expression: `^[0-9]{8}\|[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$` For example: `f2fb30e5-4ab6-4a29-b3c1-c7264259ff1c`

Request headers

Request headers Table
Name	Description
Accept required	Specifies the response format and the version of the API to be used. For example: `application/vnd.hmrc.1.0+json`
Authorization required	An OAuth 2.0 Bearer Token with the `read:self-assessment-assist` scope. For example: `Bearer bb7fed3fe10dd235a2ccda3d50fb`

Responses

HTTP status 200 (OK)

Response headers

Response headers Table
Name	Description
X-CorrelationId required	Unique ID for operation tracking String, 36 characters. For example: `c75f40a6-a3df-4429-a697-471eeec46435`

See also fraud prevention.

{
  "reportId": "f2fb30e5-4ab6-4a29-b3c1-c7264259ff1c",
  "messages": [
    {
      "title": "Turnover and Cost of Sales",
      "body": "Your cost of sales (12000) is greater than your actual income (4000). This may be an error.",
      "action": "Please read our guidance and consider amending Box 10 of your submission.",
      "links": [
        {
          "title": "Our guidance on Turnover and Expenses can be read here.",
          "url": "https://www.gov.uk/expenses-if-youre-self-employed"
        }
      ],
      "path": "general/total_declared_turnover"
    }
  ],
  "nino": "TC663795B",
  "taxYear": "2017-18",
  "calculationId": "f2fb30e5-4ab6-4a29-b3c1-c7264259ff1c",
  "correlationId": "7X57CKG72JVNSSS9SALT"
}

Response table
Name	Description
reportId string required	The unique ID (UUID) of the report. Must conform to the regular expression `^[0-9]{8}\|[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$` For example: `f2fb30e5-4ab6-4a29-b3c1-c7264259ff1c`
messages array optional	The body contains the message for the customer. For example: `[ { ",Turnover and Cost of Sales", "Your cost of sales (12000) is greater than your actual income (4000). This may be an error." }, .. etc]]`
title string required	Title of message For example: `Turnover and Cost of Sales`
body string required	The body contains the message for the customer. For example: `Your cost of sales (12000) is greater than your actual income (4000). This may be an error.`
action string optional	The recommend action the customer should take. For example: `Please read our guidance and consider amending Box 10 of your submission.`
links array optional	A list of help or support 'links' associated with the message body. For example: `[ { ",Turnover and Cost of Sales", "Your cost of sales (12000) is greater than your actual income (4000). This may be an error." }, .. etc]]`
title string optional	The title text that appears before the links. For example: `Our guidance on Turnover and Expenses can be read here.`
url string optional	The URL of support or help link. For example: `https://www.gov.uk/expenses-if-youre-self-employed`
path string required	The HTTP path to guidance provided by HMRC. For example: `general/total_declared_turnover`
nino string required	National Insurance number, in the format AA999999A. For example: `TC663795B`
taxYear string required	The tax year the data applies to, for example, 2021-22. The start year and end year must not span two tax years. No gaps are allowed, for example, 2020-22 is not valid. For example: `2017-18`
calculationId string required	The unique identifier for the calculation. Must conform the regular expression: `^[0-9]{8}\|[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$` For example: `f2fb30e5-4ab6-4a29-b3c1-c7264259ff1c`
correlationId string required	The correlationId of the report. For example: `7X57CKG72JVNSSS9SALT`

Error scenarios

Error scenarios table
Scenario	HTTP status	Code
The format of the supplied NINO field is not valid	400 (Bad Request)	FORMAT_NINO
The format of the supplied CalculationID is not valid	400 (Bad Request)	FORMAT_CALC_ID
Calculation ID was not found	404 (Not Found)	MATCHING_RESOURCE_NOT_FOUND
The client and/or agent is not authorised. This is normally because: the client is not subscribed to MTD, the agent is not subscribed to Agent Services, or the client has not authorised the agent to act on their behalf	403 (Forbidden)	CLIENT_OR_AGENT_NOT_AUTHORISED
Invalid Authentication information provided	401 (Unauthorized)	INVALID_CREDENTIALS

For error scenarios that are common across all APIs, and for error formats, see our reference guide.

Close Section

Acknowledge a HMRC Self Assessment Assist Report

POST

This endpoint allows a developer to acknowledge that the given report has been read by the customer or agent.

Authorisation

This endpoint is user-restricted and requires an Authorization header containing an OAuth 2.0 Bearer Token with the write:self-assessment-assist scope.

Path parameters

Path parameters table
Name	Description
nino string required	National Insurance number, in the format AA999999A. For example: `TC663795B`
reportId string required	The unique identifier for the report. Must conform to the regular expression: ^[0-9]{8}\|[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$ For example: `f2fb30e5-4ab6-4a29-b3c1-c7264259ff1c`
correlationId string required	The alphanumeric correlation ID of the report. For example: `7X57CKG72JVNSSS9SALT`

Request headers

Request headers Table
Name	Description
Authorization required	An OAuth 2.0 Bearer Token with the `write:self-assessment-assist` scope. For example: `Bearer bb7fed3fe10dd235a2ccda3d50fb`

Responses

HTTP status 204 (No Content)

Error scenarios

Error scenarios table
Scenario	HTTP status	Code
The format of the supplied NINO field is not valid	400 (Bad Request)	FORMAT_NINO
The format of the supplied reportID is not valid.	400 (Bad Request)	FORMAT_REPORT_ID
Calculation ID was not found	404 (Not Found)	MATCHING_RESOURCE_NOT_FOUND
The client and/or agent is not authorised. This is normally because: the client is not subscribed to MTD, the agent is not subscribed to Agent Services, or the client has not authorised the agent to act on their behalf	403 (Forbidden)	CLIENT_OR_AGENT_NOT_AUTHORISED

For error scenarios that are common across all APIs, and for error formats, see our reference guide.

Close Section

Self Assessment Assist (MTD) API

Overview

Send fraud prevention data

Versioning

Errors

Changelog

Support

Testing

Endpoints

Self Assessment Assist

Self Assessment Assist resources

Authorisation

Path parameters

Request headers

Responses

HTTP status 200 (OK)

Response headers

Error scenarios

Authorisation

Path parameters

Request headers

Responses

HTTP status 204 (No Content)

Error scenarios