Custom Estimators

If the built-in estimators don’t fit your requirements, you can implement your own by subclassing ComplexityEstimator and overriding get_field_complexity.

---

The Interface

from graphql_complexity import ComplexityEstimator


class MyEstimator(ComplexityEstimator):
    def get_field_complexity(self, node, type_info, path) -> int:
        ...

Method Parameters

Parameter	Description
node	The AST FieldNode currently being visited
type_info	A TypeInfo object with schema type information for the current node
path	A list of field names representing the current path from the root

The method must return an int — the complexity score for that single field.

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Example: Field-Name Based Pricing

Charge a fixed high cost for a specific field, and a default of 1 for everything else:

from graphql_complexity import ComplexityEstimator, get_complexity
from graphql import build_schema


class FieldNameEstimator(ComplexityEstimator):
    def get_field_complexity(self, node, type_info, path) -> int:
        if node.name.value == "expensiveField":
            return 100
        return 1


schema = build_schema("""
    type Query {
        cheapField: String
        expensiveField: String
    }
""")

query = "{ cheapField expensiveField }"

estimator = FieldNameEstimator()
complexity = get_complexity(query=query, schema=schema, estimator=estimator)
print(complexity)  # 101

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Example: Depth-Aware Pricing

Use the path argument to charge more for deeply nested fields:

from graphql_complexity import ComplexityEstimator


class DepthEstimator(ComplexityEstimator):
    def get_field_complexity(self, node, type_info, path) -> int:
        depth = len(path)
        return depth * 2  # cost grows with depth

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Example: Type-Aware Pricing

Inspect type_info to assign cost based on the GraphQL type being returned:

from graphql_complexity import ComplexityEstimator
from graphql import GraphQLList


class TypeAwareEstimator(ComplexityEstimator):
    def get_field_complexity(self, node, type_info, path) -> int:
        # List fields are more expensive
        if isinstance(type_info.get_type(), GraphQLList):
            return 10
        return 1

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Tips

• Keep get_field_complexity pure and fast — it is called once per field per query.

• Return 0 for fields you want to treat as free (e.g. __typename).

• You can combine multiple heuristics inside a single estimator.