> ## Documentation Index
> Fetch the complete documentation index at: https://developers.circle.com/llms.txt
> Use this file to discover all available pages before exploring further.

# JSON Schema

CPN uses [JSON Schema](https://json-schema.org/) to define and validate the
structure of JSON data used to pass RFI data. A JSON Schema is a blueprint for
the compliance data that OFIs must provide. CPN uses the
[Draft 2020-12](https://json-schema.org/draft/2020-12) version of the JSON
Schema standard.

Using JSON Schema to define the structure of this data has the following
benefits:

* **Clarity:** the schema defines every requirement programmatically, including
  required fields, data types, formats, and structures. This eliminates
  guesswork.
* **Client-side validation:** OFIs can validate their response against the
  schema before making the API call, providing instant feedback for developers
  and preventing common integration errors.
* **Rich data structures:** schemas support complex requirements like nested
  address objects and conditional logic.

## Interpreting JSON Schema

When you call the
[get details for an RFI endpoint](/api-reference/cpn/cpn-platform/get-rfi), the
API returns the JSON Schema for the required response data. The following are
key parts of the schemas to understand when reading them:

* `properties`: defines the fields you can provide in your JSON response
* `required`: contains a list of field names that must be present in the
  response
* `$defs` and `$ref`: usable complex objects (defined in `$defs` and referenced
  using the `$ref` directive)

## Client-side validation

JSON Schema allows you to validate your response before sending it to the API.
CPN expects that OFIs perform client-side validation against the provided schema
before submitting a response to CPN. Doing so provides a first line of defense
to reduce API errors and failed payments.

Common libraries for JSON Schema validation are:

* **Java:**
  [`networknt/json-schema-validator`](https://github.com/networknt/json-schema-validator)
* **Python:**
  [`jsonschema`](https://python-jsonschema.readthedocs.io/en/stable/)
* **Node.js:** [`ajv`](https://ajv.js.org/)

### Additional validation

JSON Schema validates structure and format only. You are still responsible for
ensuring the data is contextually correct. The schema ensures that you send the
data in the correct shape; you ensure the data is accurate. For example, you can
[validate CNPJ and CPF numbers using their check digits](/cpn/references/compliance/validating-brazil-tax-account-id)
or [validate IBAN account numbers](/cpn/references/compliance/validating-iban).