Request Syntax URI Request Parameters Request Body Response Syntax Response Elements Errors See Also

EvaluateFeature

Important

End of support notice: On October 16, 2025, AWS will discontinue support for CloudWatch Evidently. After October 16, 2025, you will no longer be able to access the Evidently console or CloudWatch Evidently resources.

This operation assigns a feature variation to one given user session. You pass in an entityID that represents the user. Evidently then checks the evaluation rules and assigns the variation.

The first rules that are evaluated are the override rules. If the user's entityID matches an override rule, the user is served the variation specified by that rule.

If there is a current launch with this feature that uses segment overrides, and if the user session's evaluationContext matches a segment rule defined in a segment override, the configuration in the segment overrides is used. For more information about segments, see CreateSegment and Use segments to focus your audience.

If there is a launch with no segment overrides, the user might be assigned to a variation in the launch. The chance of this depends on the percentage of users that are allocated to that launch. If the user is enrolled in the launch, the variation they are served depends on the allocation of the various feature variations used for the launch.

If the user is not assigned to a launch, and there is an ongoing experiment for this feature, the user might be assigned to a variation in the experiment. The chance of this depends on the percentage of users that are allocated to that experiment.

If the experiment uses a segment, then only user sessions with evaluationContext values that match the segment rule are used in the experiment.

If the user is enrolled in the experiment, the variation they are served depends on the allocation of the various feature variations used for the experiment.

If the user is not assigned to a launch or experiment, they are served the default variation.

Request Syntax


POST /projects/project/evaluations/feature HTTP/1.1
Content-type: application/json

{
   "entityId": "string",
   "evaluationContext": "string"
}

URI Request Parameters

The request uses the following URI parameters.

feature

The name of the feature being evaluated.

Length Constraints: Minimum length of 1. Maximum length of 127.

Pattern: ^[-a-zA-Z0-9._]*$

Required: Yes

project

The name or ARN of the project that contains this feature.

Length Constraints: Minimum length of 0. Maximum length of 2048.

Pattern: (^[a-zA-Z0-9._-]*$)|(arn:[^:]*:[^:]*:[^:]*:[^:]*:project/[a-zA-Z0-9._-]*)

Required: Yes

Request Body

The request accepts the following data in JSON format.

entityId

An internal ID that represents a unique user of the application. This entityID is checked against any override rules assigned for this feature.

Type: String

Length Constraints: Minimum length of 1. Maximum length of 512.

Pattern: .*

Required: Yes

evaluationContext

A JSON object of attributes that you can optionally pass in as part of the evaluation event sent to Evidently from the user session. Evidently can use this value to match user sessions with defined audience segments. For more information, see Use segments to focus your audience.

If you include this parameter, the value must be a JSON object. A JSON array is not supported.

Type: String

Required: No

Response Syntax


HTTP/1.1 200
Content-type: application/json

{
   "details": "string",
   "reason": "string",
   "value": { ... },
   "variation": "string"
}

Response Elements

If the action is successful, the service sends back an HTTP 200 response.

The following data is returned in JSON format by the service.

details

If this user was assigned to a launch or experiment, this field lists the launch or experiment name.

Type: String

reason

Specifies the reason that the user session was assigned this variation. Possible values include DEFAULT, meaning the user was served the default variation; LAUNCH_RULE_MATCH, if the user session was enrolled in a launch; EXPERIMENT_RULE_MATCH, if the user session was enrolled in an experiment; or ENTITY_OVERRIDES_MATCH, if the user's entityId matches an override rule.

Type: String

value

The value assigned to this variation to differentiate it from the other variations of this feature.

Type: VariableValue object

Note: This object is a Union. Only one member of this object can be specified or returned.

variation

The name of the variation that was served to the user session.

Type: String

Errors

For information about the errors that are common to all actions, see Common Errors.

AccessDeniedException

You do not have sufficient permissions to perform this action.

HTTP Status Code: 403

ResourceNotFoundException

The request references a resource that does not exist.

HTTP Status Code: 404

ThrottlingException

The request was denied because of request throttling. Retry the request.

HTTP Status Code: 429

ValidationException

The value of a parameter in the request caused an error.

HTTP Status Code: 400