This is the new *Amazon CloudFormation Template Reference Guide*. Please update your bookmarks and links. For help getting started with CloudFormation, see the [Amazon CloudFormation User Guide](https://docs.amazonaws.cn/AWSCloudFormation/latest/UserGuide/Welcome.html).

# AWS::SageMaker::Algorithm MetricDefinition
<a name="aws-properties-sagemaker-algorithm-metricdefinition"></a>

Specifies a metric that the training algorithm writes to `stderr` or `stdout`. You can view these logs to understand how your training job performs and check for any errors encountered during training. SageMaker hyperparameter tuning captures all defined metrics. Specify one of the defined metrics to use as an objective metric using the [TuningObjective](https://docs.amazonaws.cn/sagemaker/latest/APIReference/API_HyperParameterTrainingJobDefinition.html#sagemaker-Type-HyperParameterTrainingJobDefinition-TuningObjective) parameter in the `HyperParameterTrainingJobDefinition` API to evaluate job performance during hyperparameter tuning.

## Syntax
<a name="aws-properties-sagemaker-algorithm-metricdefinition-syntax"></a>

To declare this entity in your Amazon CloudFormation template, use the following syntax:

### JSON
<a name="aws-properties-sagemaker-algorithm-metricdefinition-syntax.json"></a>

```
{
  "[Name](#cfn-sagemaker-algorithm-metricdefinition-name)" : {{String}},
  "[Regex](#cfn-sagemaker-algorithm-metricdefinition-regex)" : {{String}}
}
```

### YAML
<a name="aws-properties-sagemaker-algorithm-metricdefinition-syntax.yaml"></a>

```
  [Name](#cfn-sagemaker-algorithm-metricdefinition-name): {{String}}
  [Regex](#cfn-sagemaker-algorithm-metricdefinition-regex): {{String}}
```

## Properties
<a name="aws-properties-sagemaker-algorithm-metricdefinition-properties"></a>

`Name`  <a name="cfn-sagemaker-algorithm-metricdefinition-name"></a>
The name of the metric.  
*Required*: Yes  
*Type*: String  
*Pattern*: `^.+$`  
*Minimum*: `1`  
*Maximum*: `255`  
*Update requires*: [Replacement](https://docs.amazonaws.cn/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks-update-behaviors.html#update-replacement)

`Regex`  <a name="cfn-sagemaker-algorithm-metricdefinition-regex"></a>
A regular expression that searches the output of a training job and gets the value of the metric. For more information about using regular expressions to define metrics, see [Defining metrics and environment variables](https://docs.amazonaws.cn/sagemaker/latest/dg/automatic-model-tuning-define-metrics-variables.html).  
*Required*: Yes  
*Type*: String  
*Pattern*: `^.+$`  
*Minimum*: `1`  
*Maximum*: `500`  
*Update requires*: [Replacement](https://docs.amazonaws.cn/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks-update-behaviors.html#update-replacement)