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# Validation
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Query validation tools for implementing security measures like query cost analysis and introspection control.
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## Capabilities
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### Query Cost Analysis
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```python { .api }
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cost_directive: SchemaDirectiveVisitor
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"""Directive for annotating field costs in schema."""
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cost_validator: Callable
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"""Validator function for enforcing query cost limits."""
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```
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## Usage Examples
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```python
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from ariadne.validation import cost_directive, cost_validator
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type_defs = """
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    directive @cost(complexity: Int, multipliers: [String!]) on FIELD_DEFINITION
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    type Query {
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        users: [User!]! @cost(complexity: 10)
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        user(id: ID!): User @cost(complexity: 1)
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    }
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"""
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schema = make_executable_schema(
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    type_defs,
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    query,
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    directives={"cost": cost_directive}
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)
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# Use cost validator
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result = await graphql(
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    schema,
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    query_data,
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    validation_rules=[cost_validator(maximum_cost=100)]
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)
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```