feat: Added an Fast API new endpoint to serve eval metric info

This endpoint could be used by ADK Web to dynamically know:
- What are the available eval metrics in an App
- A description of those metrics
- A value range supported by those metrics

We also update the metric registry to make it mandatory to supply these details. The goal is to improve usability and interpretability of the eval metrics.

PiperOrigin-RevId: 787277695

Author: ankursharmas

src/google/adk/cli/adk_web_server.py

@@ -64,6 +64,7 @@
 from ..evaluation.eval_metrics import EvalMetric
 from ..evaluation.eval_metrics import EvalMetricResult
 from ..evaluation.eval_metrics import EvalMetricResultPerInvocation
+from ..evaluation.eval_metrics import MetricInfo
 from ..evaluation.eval_result import EvalSetResult
 from ..evaluation.eval_set_results_manager import EvalSetResultsManager
 from ..evaluation.eval_sets_manager import EvalSetsManager
@@ -697,6 +698,24 @@ def list_eval_results(app_name: str) -> list[str]:
       """Lists all eval results for the given app."""
       return self.eval_set_results_manager.list_eval_set_results(app_name)
 
+    @app.get(
+        "/apps/{app_name}/eval_metrics",
+        response_model_exclude_none=True,
+    )
+    def list_eval_metrics(app_name: str) -> list[MetricInfo]:
+      """Lists all eval metrics for the given app."""
+      try:
+        from ..evaluation.metric_evaluator_registry import DEFAULT_METRIC_EVALUATOR_REGISTRY
+
+        # Right now we ignore the app_name as eval metrics are not tied to the
+        # app_name, but they could be moving forward.
+        return DEFAULT_METRIC_EVALUATOR_REGISTRY.get_registered_metrics()
+      except ModuleNotFoundError as e:
+        logger.exception("%s\n%s", MISSING_EVAL_DEPENDENCIES_MESSAGE, e)
+        raise HTTPException(
+            status_code=400, detail=MISSING_EVAL_DEPENDENCIES_MESSAGE
+        ) from e
+
     @app.delete("/apps/{app_name}/users/{user_id}/sessions/{session_id}")
     async def delete_session(app_name: str, user_id: str, session_id: str):
       await self.session_service.delete_session(

src/google/adk/evaluation/eval_metrics.py

@@ -49,16 +49,22 @@ class JudgeModelOptions(BaseModel):
 
   judge_model: str = Field(
       default="gemini-2.5-flash",
-      description="""The judge model to use for evaluation. It can be a model name.""",
+      description=(
+          "The judge model to use for evaluation. It can be a model name."
+      ),
   )
 
   judge_model_config: Optional[genai_types.GenerateContentConfig] = Field(
-      default=None, description="""The configuration for the judge model."""
+      default=None,
+      description="The configuration for the judge model.",
   )
 
   num_samples: Optional[int] = Field(
       default=None,
-      description="""The number of times to sample the model for each invocation evaluation.""",
+      description=(
+          "The number of times to sample the model for each invocation"
+          " evaluation."
+      ),
   )
 
 
@@ -70,15 +76,20 @@ class EvalMetric(BaseModel):
       populate_by_name=True,
   )
 
-  metric_name: str
-  """The name of the metric."""
+  metric_name: str = Field(
+      description="The name of the metric.",
+  )
 
-  threshold: float
-  """A threshold value. Each metric decides how to interpret this threshold."""
+  threshold: float = Field(
+      description=(
+          "A threshold value. Each metric decides how to interpret this"
+          " threshold."
+      ),
+  )
 
   judge_model_options: Optional[JudgeModelOptions] = Field(
       default=None,
-      description="""Options for the judge model.""",
+      description="Options for the judge model.",
   )
 
 
@@ -90,8 +101,14 @@ class EvalMetricResult(EvalMetric):
       populate_by_name=True,
   )
 
-  score: Optional[float] = None
-  eval_status: EvalStatus
+  score: Optional[float] = Field(
+      default=None,
+      description=(
+          "Score obtained after evaluating the metric. Optional, as evaluation"
+          " might not have happened."
+      ),
+  )
+  eval_status: EvalStatus = Field(description="The status of this evaluation.")
 
 
 class EvalMetricResultPerInvocation(BaseModel):
@@ -102,11 +119,71 @@ class EvalMetricResultPerInvocation(BaseModel):
       populate_by_name=True,
   )
 
-  actual_invocation: Invocation
-  """The actual invocation, usually obtained by inferencing the agent."""
+  actual_invocation: Invocation = Field(
+      description=(
+          "The actual invocation, usually obtained by inferencing the agent."
+      )
+  )
+
+  expected_invocation: Invocation = Field(
+      description=(
+          "The expected invocation, usually the reference or golden invocation."
+      )
+  )
 
-  expected_invocation: Invocation
-  """The expected invocation, usually the reference or golden invocation."""
+  eval_metric_results: list[EvalMetricResult] = Field(
+      default=[],
+      description="Eval resutls for each applicable metric.",
+  )
+
+
+class Interval(BaseModel):
+  """Represents a range of numeric values, e.g. [0 ,1] or (2,3) or [-1, 6)."""
+
+  min_value: float = Field(description="The smaller end of the interval.")
+
+  open_at_min: bool = Field(
+      default=False,
+      description=(
+          "The interval is Open on the min end. The default value is False,"
+          " which means that we assume that the interval is Closed."
+      ),
+  )
+
+  max_value: float = Field(description="The larger end of the interval.")
+
+  open_at_max: bool = Field(
+      default=False,
+      description=(
+          "The interval is Open on the max end. The default value is False,"
+          " which means that we assume that the interval is Closed."
+      ),
+  )
 
-  eval_metric_results: list[EvalMetricResult] = []
-  """Eval resutls for each applicable metric."""
+
+class MetricValueInfo(BaseModel):
+  """Information about the type of metric value."""
+
+  interval: Optional[Interval] = Field(
+      default=None,
+      description="The values represented by the metric are of type interval.",
+  )
+
+
+class MetricInfo(BaseModel):
+  """Information about the metric that are used for Evals."""
+
+  model_config = ConfigDict(
+      alias_generator=alias_generators.to_camel,
+      populate_by_name=True,
+  )
+
+  metric_name: str = Field(description="The name of the metric.")
+
+  description: str = Field(
+      default=None, description="A 2 to 3 line description of the metric."
+  )
+
+  metric_value_info: MetricValueInfo = Field(
+      description="Information on the nature of values supported by the metric."
+  )

src/google/adk/evaluation/final_response_match_v1.py

@@ -22,18 +22,39 @@
 
 from .eval_case import Invocation
 from .eval_metrics import EvalMetric
+from .eval_metrics import Interval
+from .eval_metrics import MetricInfo
+from .eval_metrics import MetricValueInfo
+from .eval_metrics import PrebuiltMetrics
 from .evaluator import EvalStatus
 from .evaluator import EvaluationResult
 from .evaluator import Evaluator
 from .evaluator import PerInvocationResult
 
 
 class RougeEvaluator(Evaluator):
-  """Calculates the ROUGE-1 metric to compare responses."""
+  """Evaluates if agent's final response matches a golden/expected final response using Rouge_1 metric.
+
+  Value range for this metric is [0,1], with values closer to 1 more desirable.
+  """
 
   def __init__(self, eval_metric: EvalMetric):
     self._eval_metric = eval_metric
 
+  @staticmethod
+  def get_metric_info() -> MetricInfo:
+    return MetricInfo(
+        metric_name=PrebuiltMetrics.RESPONSE_MATCH_SCORE.value,
+        description=(
+            "This metric evaluates if the agent's final response matches a"
+            " golden/expected final response using Rouge_1 metric. Value range"
+            " for this metric is [0,1], with values closer to 1 more desirable."
+        ),
+        metric_value_info=MetricValueInfo(
+            interval=Interval(min_value=0.0, max_value=1.0)
+        ),
+    )
+
   @override
   def evaluate_invocations(
       self,

src/google/adk/evaluation/final_response_match_v2.py

@@ -24,6 +24,10 @@
 from ..utils.feature_decorator import experimental
 from .eval_case import Invocation
 from .eval_metrics import EvalMetric
+from .eval_metrics import Interval
+from .eval_metrics import MetricInfo
+from .eval_metrics import MetricValueInfo
+from .eval_metrics import PrebuiltMetrics
 from .evaluator import EvalStatus
 from .evaluator import EvaluationResult
 from .evaluator import PerInvocationResult
@@ -146,6 +150,20 @@ def __init__(
     if self._eval_metric.judge_model_options.num_samples is None:
       self._eval_metric.judge_model_options.num_samples = _DEFAULT_NUM_SAMPLES
 
+  @staticmethod
+  def get_metric_info() -> MetricInfo:
+    return MetricInfo(
+        metric_name=PrebuiltMetrics.FINAL_RESPONSE_MATCH_V2.value,
+        description=(
+            "This metric evaluates if the agent's final response matches a"
+            " golden/expected final response using LLM as a judge. Value range"
+            " for this metric is [0,1], with values closer to 1 more desirable."
+        ),
+        metric_value_info=MetricValueInfo(
+            interval=Interval(min_value=0.0, max_value=1.0)
+        ),
+    )
+
   @override
   def format_auto_rater_prompt(
       self, actual_invocation: Invocation, expected_invocation: Invocation
@@ -185,8 +203,7 @@ def aggregate_per_invocation_samples(
     tie, consider the result to be invalid.
 
     Args:
-      per_invocation_samples: Samples of per-invocation results to
-        aggregate.
+      per_invocation_samples: Samples of per-invocation results to aggregate.
 
     Returns:
       If there is a majority of valid results, return the first valid result.

src/google/adk/evaluation/metric_evaluator_registry.py

@@ -17,7 +17,9 @@
 import logging
 
 from ..errors.not_found_error import NotFoundError
+from ..utils.feature_decorator import experimental
 from .eval_metrics import EvalMetric
+from .eval_metrics import MetricInfo
 from .eval_metrics import MetricName
 from .eval_metrics import PrebuiltMetrics
 from .evaluator import Evaluator
@@ -29,10 +31,11 @@
 logger = logging.getLogger("google_adk." + __name__)
 
 
+@experimental
 class MetricEvaluatorRegistry:
   """A registry for metric Evaluators."""
 
-  _registry: dict[str, type[Evaluator]] = {}
+  _registry: dict[str, tuple[type[Evaluator], MetricInfo]] = {}
 
   def get_evaluator(self, eval_metric: EvalMetric) -> Evaluator:
     """Returns an Evaluator for the given metric.
@@ -48,15 +51,18 @@ def get_evaluator(self, eval_metric: EvalMetric) -> Evaluator:
     if eval_metric.metric_name not in self._registry:
       raise NotFoundError(f"{eval_metric.metric_name} not found in registry.")
 
-    return self._registry[eval_metric.metric_name](eval_metric=eval_metric)
+    return self._registry[eval_metric.metric_name][0](eval_metric=eval_metric)
 
   def register_evaluator(
-      self, metric_name: MetricName, evaluator: type[Evaluator]
+      self,
+      metric_info: MetricInfo,
+      evaluator: type[Evaluator],
   ):
-    """Registers an evaluator given the metric name.
+    """Registers an evaluator given the metric info.
 
     If a mapping already exist, then it is updated.
     """
+    metric_name = metric_info.metric_name
     if metric_name in self._registry:
       logger.info(
           "Updating Evaluator class for %s from %s to %s",
@@ -65,31 +71,45 @@ def register_evaluator(
           evaluator,
       )
 
-    self._registry[str(metric_name)] = evaluator
+    self._registry[str(metric_name)] = (evaluator, metric_info)
+
+  def get_registered_metrics(
+      self,
+  ) -> list[MetricInfo]:
+    """Returns a list of MetricInfo about the metrics registered so far."""
+    return [
+        evaluator_and_metric_info[1].model_copy(deep=True)
+        for _, evaluator_and_metric_info in self._registry.items()
+    ]
 
 
 def _get_default_metric_evaluator_registry() -> MetricEvaluatorRegistry:
   """Returns an instance of MetricEvaluatorRegistry with standard metrics already registered in it."""
   metric_evaluator_registry = MetricEvaluatorRegistry()
 
   metric_evaluator_registry.register_evaluator(
-      metric_name=PrebuiltMetrics.TOOL_TRAJECTORY_AVG_SCORE.value,
+      metric_info=TrajectoryEvaluator.get_metric_info(),
       evaluator=TrajectoryEvaluator,
   )
+
   metric_evaluator_registry.register_evaluator(
-      metric_name=PrebuiltMetrics.RESPONSE_EVALUATION_SCORE.value,
+      metric_info=ResponseEvaluator.get_metric_info(
+          PrebuiltMetrics.RESPONSE_EVALUATION_SCORE.value
+      ),
       evaluator=ResponseEvaluator,
   )
   metric_evaluator_registry.register_evaluator(
-      metric_name=PrebuiltMetrics.RESPONSE_MATCH_SCORE.value,
+      metric_info=ResponseEvaluator.get_metric_info(
+          PrebuiltMetrics.RESPONSE_MATCH_SCORE.value
+      ),
       evaluator=ResponseEvaluator,
   )
   metric_evaluator_registry.register_evaluator(
-      metric_name=PrebuiltMetrics.SAFETY_V1.value,
+      metric_info=SafetyEvaluatorV1.get_metric_info(),
       evaluator=SafetyEvaluatorV1,
   )
   metric_evaluator_registry.register_evaluator(
-      metric_name=PrebuiltMetrics.FINAL_RESPONSE_MATCH_V2.value,
+      metric_info=FinalResponseMatchV2Evaluator.get_metric_info(),
       evaluator=FinalResponseMatchV2Evaluator,
   )