# JSON, XML and YAML data formats

*MuleSoft Integration Foundations Study Guide · Recognize and interpret essential integration concepts and terminology · Last updated November 2, 2026 · https://www.certifyforce.com/study-guide/mulesoft-integration-foundations/essential-integration-concepts-and-terminology/json-xml-and-yaml-data-formats*

How JSON, XML and YAML structure data (objects and arrays, repeated elements with attributes and namespaces, indented mappings and sequences), which ones DataWeave reads and writes in transformations, and why YAML and .properties files hold Mule configuration properties.

- Certification: Salesforce MuleSoft Integration Foundations
- Exam section: Recognize and interpret essential integration concepts and terminology
- Study guide: https://www.certifyforce.com/study-guide/mulesoft-integration-foundations

**Official exam objective:**

> Recognize the differences between common data formats (for example, XML, YAML, and JSON) used in transformations and configuration files.

## What the exam expects

- Recognize a JSON, XML or YAML document from its structure and name the value types each one holds.
- Describe how XML and JSON differ when one is transformed into the other (collections, attributes, namespaces, types).
- Identify YAML and .properties as the file formats for Mule configuration properties.
- Explain that DataWeave reads and writes many formats, each identified by a MIME type, so one script converts between them.

Key terms:
- **JSON**: a format of objects and arrays holding strings, numbers, booleans and null.
- **XML**: a format of nested elements, where collections are repeated elements and elements can carry attributes and namespaces.
- **YAML**: a human-readable format of indented mappings and sequences.
- **MIME type**: the identifier of a format, such as `application/json`.
- **Configuration properties**: externalized settings that Mule flows read through `${...}` placeholders.

## Key facts

| Fact | Detail | Source |
|---|---|---|
| JSON types | String, Boolean, Number, Null, Object, Array | [JSON Format](https://docs.mulesoft.com/dataweave/latest/dataweave-formats-json) |
| XML collections | Repeated (unbounded) elements | [XML Format](https://docs.mulesoft.com/dataweave/latest/dataweave-formats-xml) |
| XML extras | Namespaces, CDATA, `xsi:types` | [XML Format](https://docs.mulesoft.com/dataweave/latest/dataweave-formats-xml) |
| YAML types | String, Boolean, Number, Nil, Mapping, Sequences | [YAML Format](https://docs.mulesoft.com/dataweave/latest/dataweave-formats-yaml) |
| Format MIME types | `application/json`, `application/xml`, `application/yaml`, `application/csv` | [Supported Data Formats](https://docs.mulesoft.com/dataweave/latest/dataweave-formats) |
| Config properties file types | `.yaml` and `.properties` only | [Configuring Properties](https://docs.mulesoft.com/mule-runtime/latest/configuring-properties) |
| Config property value type | String only, in both file types | [Configuring Properties](https://docs.mulesoft.com/mule-runtime/latest/configuring-properties) |
| Duplicate property | The first definition is preserved | [Configuring Properties](https://docs.mulesoft.com/mule-runtime/latest/configuring-properties) |

## Check yourself

- Why would a DataWeave reader index a large file instead of loading it into memory?
- When DataWeave represents JSON input in its own dw format, what changes?
- When an XML file contains a doctype declaration, are DTDs processed by default?
- Which MIME types does the DataWeave YAML format accept besides `application/yaml`?

## Sources

- [Supported Data Formats](https://docs.mulesoft.com/dataweave/latest/dataweave-formats)
- [JSON Format](https://docs.mulesoft.com/dataweave/latest/dataweave-formats-json)
- [XML Format](https://docs.mulesoft.com/dataweave/latest/dataweave-formats-xml)
- [YAML Format](https://docs.mulesoft.com/dataweave/latest/dataweave-formats-yaml)
- [Configuring Properties](https://docs.mulesoft.com/mule-runtime/latest/configuring-properties)

## About the full unit

The "Core concepts", "Exam traps" and "Worked scenario" sections of this unit, its 4 linked practice questions, and unlimited timed mock exams are included with the MuleSoft Integration Foundations pack (USD $19): https://www.certifyforce.com/practice-exams