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These requirements and formats apply to every Platform API request and response.

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Headers

The legacy header Accept: application/vnd.mx.api.v1+json still works and requests v20111101. Move to Accept: application/json with an Accept-Version header.

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Data format

Requests and responses use JSON, including error responses (see Errors). The exceptions are:
  • Download Statement PDF returns a PDF file.
  • Some responses, such as 204 No Content, have no body.
  • Encrypted responses return an encrypted JWE string.
Requests must use UTF-8 character encoding.

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Request bodies

PUT request bodies can’t be empty. Include at least one parameter inside the body’s root object, even when no parameter is required. An empty PUT body returns 400 Bad Request.

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Boolean fields

Boolean fields accept only true or false. Don’t use 0 or 1.

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Dates and times

Dates and times use ISO 8601 format:
  • Fields that end in _on are dates without a time, for example 2018-07-18.
  • Fields that end in _at are dates with a time and UTC offset, for example 2025-02-13T18:08:00+00:00.
In v20250224 only, the date filters on List Transactions endpoints use Unix timestamps. See the Upgrade Guide.

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Numbers

Some fields, such as account balances, have limits on decimal numbers, given as precision and scale (for example, 14,2). Precision is the total number of digits, and scale is the number of digits to the right of the decimal point. For example, 538.46 has a precision and scale of 5,2.

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Identifiers and metadata

Don’t store sensitive information in metadata, such as usernames, passwords, or account numbers.
Many resources you create through the API accept an optional id and an optional metadata field.
  • id: Your own unique identifier for the resource. Use it to make sure a resource is created only once, or to match MX data with data on your platform. Creating a resource with an id that already exists returns 409 Conflict.
  • metadata: A string you can use to store additional data about the resource, such as a JSON-encoded string. MX doesn’t use it.

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Pagination

Endpoints that return lists are paginated. Use these query parameters to control which page you get and how many records it contains: Each list response includes a pagination object:

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Special characters in responses

Because of the financial nature of the data, string fields may contain special characters such as ', <, >, ", and =. For example, an account might be named Mortgage Loan <= 15 Years. Sanitize or encode API output before you display it, for example by HTML-encoding it before rendering it in a web view.

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Caching

Some resources, such as institutions, can change at any time. Avoid caching lists of these resources. If you need to cache them, refresh the cache at least once a day.