XSD Schemas

X4 ships 41 XSD schema files that formally define the structure of its XML files. These are invaluable for validation during mod development.

Extracting schemas

x4cat extract "/path/to/X4 Foundations" -o ./schemas -g '*.xsd'

Schema hierarchy

md/md.xsd                    -- includes ../libraries/md.xsd
aiscripts/aiscripts.xsd      -- includes ../libraries/aiscripts.xsd
libraries/md.xsd              -- includes common.xsd
libraries/aiscripts.xsd       -- includes common.xsd
libraries/common.xsd          -- base types and expressions (40K lines)
libraries/diff.xsd            -- diff patching operations
libraries/libraries.xsd       -- library file structures

Key schemas

Schema	Lines	Purpose
libraries/common.xsd	40,572	Base types, expression language, variables
libraries/md.xsd	4,919	Mission Director elements and attributes
libraries/aiscripts.xsd	–	AI script elements
libraries/diff.xsd	–	Diff patch operations (add/replace/remove)
libraries/parameters.xsd	–	Game parameter definitions
libraries/libraries.xsd	–	Library XML structures

Validation

Full XSD validation is slow (~70 seconds) due to the size of common.xsd. For development, use structural checks (correct root element, required attributes) and reserve full XSD validation for pre-release verification.

# Fast: structural validation
xmllint --noout src/md/*.xml

# Slow but thorough: full XSD validation
xmllint --schema schemas/md/md.xsd --noout src/md/my_script.xml

Or use the extension_poc template’s make schema-validate target.

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