class Evaluator (construct) 🔹

Language	Type name
.NET	Amazon.CDK.AWS.Bedrock.Agentcore.Alpha.Evaluator
Go	github.com/aws/aws-cdk-go/awsbedrockagentcorealpha/v2#Evaluator
Java	software.amazon.awscdk.services.bedrock.agentcore.alpha.Evaluator
Python	aws_cdk.aws_bedrock_agentcore_alpha.Evaluator
TypeScript (source)	@aws-cdk/aws-bedrock-agentcore-alpha » Evaluator

Implements IConstruct, IDependable, IResource, IEnvironmentAware, IEvaluator, IEvaluatorRef

A custom evaluator for Amazon Bedrock AgentCore.

Custom evaluators enable you to define evaluation logic tailored to your specific use cases. Supports two evaluation strategies:

• LLM-as-a-Judge: Uses a foundation model with custom instructions and a rating scale.
• Code-based: Uses a Lambda function for custom evaluation logic.

Custom evaluators are used with OnlineEvaluationConfig via EvaluatorReference.custom().

Example

// Create a custom LLM-as-a-Judge evaluator
const evaluator = new agentcore.Evaluator(this, 'MyEvaluator', {
  evaluatorName: 'my_custom_evaluator',
  level: agentcore.EvaluationLevel.SESSION,
  evaluatorConfig: agentcore.EvaluatorConfig.llmAsAJudge({
    instructions: 'Evaluate whether the agent response is helpful and accurate.',
    modelId: 'us.anthropic.claude-sonnet-4-6',
    ratingScale: agentcore.EvaluatorRatingScale.categorical([
      { label: 'Good', definition: 'The response is helpful and accurate.' },
      { label: 'Bad', definition: 'The response is not helpful or contains errors.' },
    ]),
  }),
});

// Use the custom evaluator in an online evaluation configuration
new agentcore.OnlineEvaluationConfig(this, 'MyEvaluation', {
  onlineEvaluationConfigName: 'my_evaluation',
  evaluators: [
    agentcore.EvaluatorReference.builtin(agentcore.BuiltinEvaluator.HELPFULNESS),
    agentcore.EvaluatorReference.custom(evaluator),
  ],
  dataSource: agentcore.DataSourceConfig.fromCloudWatchLogs({
    logGroupNames: ['/aws/bedrock-agentcore/my-agent'],
    serviceNames: ['my-agent.default'],
  }),
});

Initializer

new Evaluator(scope: Construct, id: string, props: EvaluatorProps)

Parameters

• scope Construct
• id string
• props EvaluatorProps

Construct Props

Name	Type	Description
evaluatorConfig🔹	EvaluatorConfig	The configuration that defines how the evaluator assesses agent performance.
evaluatorName🔹	string	The name of the evaluator.
level🔹	EvaluationLevel	The level at which the evaluator assesses agent performance.
description?🔹	string	The description of the evaluator.

---

evaluatorConfig🔹

Type: EvaluatorConfig

The configuration that defines how the evaluator assesses agent performance.

Use EvaluatorConfig.llmAsAJudge() for model-based evaluation or EvaluatorConfig.codeBased() for Lambda-based evaluation.

---

evaluatorName🔹

Type: string

The name of the evaluator.

Must be unique within your account. Valid characters are a-z, A-Z, 0-9, _ (underscore). Must start with a letter and can be up to 48 characters long.

---

level🔹

Type: EvaluationLevel

The level at which the evaluator assesses agent performance.

Determines what granularity of data the evaluator operates on: tool call, trace (single request-response), or session (full conversation).

---

description?🔹

Type: string (optional, default: No description)

The description of the evaluator.

Properties

Name	Type	Description
env🔹	ResourceEnvironment	The environment this resource belongs to.
evaluatorArn🔹	string	The ARN of the evaluator.
evaluatorId🔹	string	The unique identifier of the evaluator.
evaluatorName🔹	string	The name of the evaluator.
evaluatorRef🔹	EvaluatorReference	A reference to this Evaluator resource.
node🔹	Node	The tree node.
stack🔹	Stack	The stack in which this resource is defined.
createdAt?🔹	string	The timestamp when the evaluator was created.
status?🔹	string	The lifecycle status of the evaluator.
updatedAt?🔹	string	The timestamp when the evaluator was last updated.
static PROPERTY_INJECTION_ID🔹	string	Uniquely identifies this class.

---

env🔹

Type: ResourceEnvironment

The environment this resource belongs to.

For resources that are created and managed in a Stack (those created by creating new class instances like new Role(), new Bucket(), etc.), this is always the same as the environment of the stack they belong to.

For referenced resources (those obtained from referencing methods like Role.fromRoleArn(), Bucket.fromBucketName(), etc.), they might be different than the stack they were imported into.

---

evaluatorArn🔹

Type: string

The ARN of the evaluator.

---

evaluatorId🔹

Type: string

The unique identifier of the evaluator.

---

evaluatorName🔹

Type: string

The name of the evaluator.

---

evaluatorRef🔹

Type: EvaluatorReference

A reference to this Evaluator resource.

---

node🔹

Type: Node

The tree node.

---

stack🔹

Type: Stack

The stack in which this resource is defined.

---

createdAt?🔹

Type: string (optional)

The timestamp when the evaluator was created.

---

status?🔹

Type: string (optional)

The lifecycle status of the evaluator.

---

updatedAt?🔹

Type: string (optional)

The timestamp when the evaluator was last updated.

---

static PROPERTY_INJECTION_ID🔹

Type: string

Uniquely identifies this class.

Methods

Name	Description
applyRemovalPolicy(policy)🔹	Apply the given removal policy to this resource.
grant(grantee, ...actions)🔹	Grants IAM actions to the IAM Principal.
toString()🔹	Returns a string representation of this construct.
with(...mixins)🔹	Applies one or more mixins to this construct.
static fromEvaluatorArn(scope, id, evaluatorArn)🔹	Import an existing Evaluator by its ARN.
static fromEvaluatorAttributes(scope, id, attrs)🔹	Import an existing Evaluator from its attributes.
static fromEvaluatorId(scope, id, evaluatorId)🔹	Import an existing Evaluator by its ID.

---

applyRemovalPolicy(policy)🔹

public applyRemovalPolicy(policy: RemovalPolicy): void

Parameters

• policy RemovalPolicy

Apply the given removal policy to this resource.

The Removal Policy controls what happens to this resource when it stops being managed by CloudFormation, either because you've removed it from the CDK application or because you've made a change that requires the resource to be replaced.

The resource can be deleted (RemovalPolicy.DESTROY), or left in your AWS account for data recovery and cleanup later (RemovalPolicy.RETAIN).

---

grant(grantee, ...actions)🔹

public grant(grantee: IGrantable, ...actions: string[]): Grant

Parameters

• grantee IGrantable — - The IAM principal to grant permissions to.
• actions string — - The actions to grant.

Returns

• Grant

Grants IAM actions to the IAM Principal.

[disable-awslint:no-grants]

---

toString()🔹

public toString(): string

Returns

• string

Returns a string representation of this construct.

---

with(...mixins)🔹

public with(...mixins: IMixin[]): IConstruct

Parameters

• mixins IMixin

Returns

• IConstruct

Applies one or more mixins to this construct.

Mixins are applied in order. The list of constructs is captured at the start of the call, so constructs added by a mixin will not be visited. Use multiple with() calls if subsequent mixins should apply to added constructs.

---

static fromEvaluatorArn(scope, id, evaluatorArn)🔹

public static fromEvaluatorArn(scope: Construct, id: string, evaluatorArn: string): IEvaluator

Parameters

• scope Construct — - The construct scope.
• id string — - Construct identifier.
• evaluatorArn string — - The evaluator ARN to import.

Returns

• IEvaluator

Import an existing Evaluator by its ARN.

---

static fromEvaluatorAttributes(scope, id, attrs)🔹

public static fromEvaluatorAttributes(scope: Construct, id: string, attrs: EvaluatorAttributes): IEvaluator

Parameters

• scope Construct — - The construct scope.
• id string — - Construct identifier.
• attrs EvaluatorAttributes — - The evaluator attributes.

Returns

• IEvaluator

Import an existing Evaluator from its attributes.

---

static fromEvaluatorId(scope, id, evaluatorId)🔹

public static fromEvaluatorId(scope: Construct, id: string, evaluatorId: string): IEvaluator

Parameters

• scope Construct — - The construct scope.
• id string — - Construct identifier.
• evaluatorId string — - The evaluator ID to import.

Returns

• IEvaluator

Import an existing Evaluator by its ID.