# EvaluationSubject A type that represents the output the system under test produces. ``` protocol EvaluationSubject ``` ## Overview Conform to this protocol to define custom subject types. The primary concrete conformance is [`ModelSubject`](/documentation/Evaluations/ModelSubject), which carries a value and an optional transcript for tool-call evaluation. ```swift struct MySubject: EvaluationSubject { var value: Value var transcript: StructuredTranscript? } ``` ## Topics ### Associated Types [`associatedtype Value : Decodable, Encodable`](/documentation/Evaluations/EvaluationSubject/Value-swift.associatedtype) The type of value the system under test produces. ### Instance Properties [`var transcript: StructuredTranscript?`](/documentation/Evaluations/EvaluationSubject/transcript) The structured transcript captured while producing the value, if any. [`var value: Self.Value`](/documentation/Evaluations/EvaluationSubject/value-swift.property) The typed value the system under test produces. ## Relationships ### Conforming Types [`ModelSubject`](/documentation/Evaluations/ModelSubject) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)