Services or capabilities described in Amazon Web Services documentation might vary by Region. To see the differences applicable to the China Regions, see Getting Started with Amazon Web Services in China (PDF).

On-demand dataset runner

The OnDemandEvaluationDatasetRunner orchestrates the entire evaluation lifecycle client-side: invoke the agent, wait for telemetry ingestion, collect spans from CloudWatch, and call the Evaluate API, all in a single run() call.

Use the on-demand runner for dev-time iteration, CI/CD pipelines, and small datasets where you need per-scenario, per-evaluator detail immediately in the response.

How it works

The runner processes scenarios in three phases:

Agent invoker

The runner requires an agent invoker, a callable that invokes your agent for a single turn. The invoker is framework-agnostic: you can call your agent via boto3 invoke_agent_runtime, a direct function call, HTTP request, or any other method.

import json
import boto3
from bedrock_agentcore.evaluation import AgentInvokerInput, AgentInvokerOutput

REGION       = "<region-code>"
AGENT_ARN    = "arn:aws:bedrock-agentcore:<region-code>:<account-id>:runtime/<agent-id>"
LOG_GROUP    = "/aws/bedrock-agentcore/runtimes/<agent-id>-DEFAULT"

agentcore_client = boto3.client("bedrock-agentcore", region_name=REGION)

def agent_invoker(invoker_input: AgentInvokerInput) -> AgentInvokerOutput:
    payload = invoker_input.payload
    if isinstance(payload, str):
        payload = json.dumps({"prompt": payload}).encode()
    elif isinstance(payload, dict):
        payload = json.dumps(payload).encode()

    print(f"[{invoker_input.session_id}] > sending payload: {payload.decode()}")
    response = agentcore_client.invoke_agent_runtime(
        agentRuntimeArn=AGENT_ARN,
        runtimeSessionId=invoker_input.session_id,
        payload=payload,
    )
    response_body = response["response"].read()
    print(f"[{invoker_input.session_id}] < received response: {response_body.decode()}")
    return AgentInvokerOutput(agent_output=json.loads(response_body))

Example

The following example loads a dataset from a JSON file and runs the on-demand evaluation. For the dataset format, see Dataset schema.

from bedrock_agentcore.evaluation import (
    OnDemandEvaluationDatasetRunner,
    EvaluationRunConfig,
    EvaluatorConfig,
    FileDatasetProvider,
    CloudWatchAgentSpanCollector,
)

# Load dataset from a local file (see Dataset schema for format)
dataset = FileDatasetProvider("dataset.json").get_dataset()

# Or load from the Dataset Management service
from bedrock_agentcore.evaluation import DatasetClient, DatasetManagementServiceProvider
ds_client = DatasetClient(region_name=REGION)
dataset = DatasetManagementServiceProvider(dataset_id="my-dataset-id", client=ds_client).get_dataset()

# Create span collector
span_collector = CloudWatchAgentSpanCollector(
    log_group_name=LOG_GROUP,
    region=REGION,
)

# Configure evaluators
config = EvaluationRunConfig(
    evaluator_config=EvaluatorConfig(
        evaluator_ids=[
            "Builtin.GoalSuccessRate",
            "Builtin.TrajectoryExactOrderMatch",
            "Builtin.Correctness",
            "Builtin.Helpfulness",
        ],
    ),
    evaluation_delay_seconds=180,
    max_concurrent_scenarios=5,
)

# Run
runner = OnDemandEvaluationDatasetRunner(region=REGION)
result = runner.run(
    agent_invoker=agent_invoker,
    dataset=dataset,
    span_collector=span_collector,
    config=config,
)

print(f"Completed: {len(result.scenario_results)} scenario(s)")

Process results:

for scenario in result.scenario_results:
    print(f"\nScenario: {scenario.scenario_id} ({scenario.status})")
    if scenario.error:
        print(f"  Error: {scenario.error}")
        continue
    for evaluator in scenario.evaluator_results:
        print(f"  {evaluator.evaluator_id}:")
        for r in evaluator.results:
            print(f"    Score: {r.get('value')}, Label: {r.get('label')}")
            ignored = r.get("ignoredReferenceInputFields", [])
            if ignored:
                print(f"    Ignored fields: {ignored}")

To save results to a file:

with open("results.json", "w") as f:
    f.write(result.model_dump_json(indent=2))

Configuration reference

Span collector

An AgentSpanCollector that retrieves telemetry spans after agent invocation. The SDK ships CloudWatchAgentSpanCollector:

from bedrock_agentcore.evaluation import CloudWatchAgentSpanCollector

span_collector = CloudWatchAgentSpanCollector(
    log_group_name="/aws/bedrock-agentcore/runtimes/<agent-id>-DEFAULT",
    region=REGION,
)

The collector queries two CloudWatch log groups (aws/spans for structural spans and the agent’s log group for conversation content), polls until spans appear, and returns them as a flat list.

Evaluation config

from bedrock_agentcore.evaluation import EvaluationRunConfig, EvaluatorConfig

config = EvaluationRunConfig(
    evaluator_config=EvaluatorConfig(
        evaluator_ids=["Builtin.Correctness", "Builtin.GoalSuccessRate"],
    ),
    evaluation_delay_seconds=180,  # Wait for CloudWatch ingestion (default: 180)
    max_concurrent_scenarios=5,    # Thread pool size (default: 5)
    simulation_config=None,        # Set SimulationConfig for simulated scenarios
)

Result structure

The runner returns an EvaluationResult with the following structure:

EvaluationResult
  └── scenario_results: List[ScenarioResult]
        ├── scenario_id: str
        ├── session_id: str
        ├── status: "COMPLETED" | "FAILED"
        ├── error: Optional[str]
        └── evaluator_results: List[EvaluatorResult]
              ├── evaluator_id: str
              └── results: List[Dict]   # Raw API responses

Each entry in results is a raw response dict from the Evaluate API, containing fields like value, label, explanation, context, tokenUsage, and ignoredReferenceInputFields. See Getting started with on-demand evaluation for the full response format.

A scenario with status FAILED means a structural problem occurred (agent invocation error, span collection failure). Individual evaluator errors within a COMPLETED scenario are recorded in the evaluator’s results list with errorCode and errorMessage fields.