Protocol Documentation
April 7, 2026 · View on GitHub
flagd/evaluation/v1/evaluation.proto
Flag evaluation API
This proto forms the basis of a flag-evaluation API. It supports single and bulk evaluation RPCs, and flags of various types, as well as establishing a stream for getting notifications about changes in a flag definition. It supports the inclusion of a "context" with each evaluation, which may contain arbitrary attributes relevant to flag evaluation.
AnyFlag
A variant type flag response.
| Field | Type | Label | Description |
|---|---|---|---|
| reason | string | The reason for the given return value, see https://openfeature.dev/docs/specification/types#resolution-details | |
| variant | string | The variant name of the returned flag value. | |
| bool_value | bool | ||
| string_value | string | ||
| double_value | double | ||
| object_value | google.protobuf.Struct | ||
| metadata | google.protobuf.Struct | Metadata for this evaluation |
EventStreamRequest
Empty stream request body
EventStreamResponse
Response body for the EventStream stream response
| Field | Type | Label | Description |
|---|---|---|---|
| type | string | String key indicating the type of event that is being received, for example, provider_ready or configuration_change | |
| data | google.protobuf.Struct | Object structure for use when sending relevant metadata to provide context to the event. Can be left unset when it is not required. |
ResolveAllRequest
Request body for bulk flag evaluation, used by the ResolveAll rpc.
| Field | Type | Label | Description |
|---|---|---|---|
| context | google.protobuf.Struct | Object structure describing the EvaluationContext used in the flag evaluation, see https://openfeature.dev/docs/reference/concepts/evaluation-context |
ResolveAllResponse
Response body for bulk flag evaluation, used by the ResolveAll rpc.
| Field | Type | Label | Description |
|---|---|---|---|
| flags | ResolveAllResponse.FlagsEntry | repeated | Object structure describing the evaluated flags for the provided context. |
| metadata | google.protobuf.Struct | Metadata for the bulk evaluation |
ResolveAllResponse.FlagsEntry
| Field | Type | Label | Description |
|---|---|---|---|
| key | string | ||
| value | AnyFlag |
ResolveBooleanRequest
Request body for boolean flag evaluation, used by the ResolveBoolean rpc.
| Field | Type | Label | Description |
|---|---|---|---|
| flag_key | string | Flag key of the requested flag. | |
| context | google.protobuf.Struct | Object structure describing the EvaluationContext used in the flag evaluation, see https://openfeature.dev/docs/reference/concepts/evaluation-context |
ResolveBooleanResponse
Response body for boolean flag evaluation. used by the ResolveBoolean rpc.
| Field | Type | Label | Description |
|---|---|---|---|
| value | bool | The response value of the boolean flag evaluation, will be unset in the case of error. | |
| reason | string | The reason for the given return value, see https://openfeature.dev/docs/specification/types#resolution-details | |
| variant | string | The variant name of the returned flag value. | |
| metadata | google.protobuf.Struct | Metadata for this evaluation |
ResolveFloatRequest
Request body for float flag evaluation, used by the ResolveFloat rpc.
| Field | Type | Label | Description |
|---|---|---|---|
| flag_key | string | Flag key of the requested flag. | |
| context | google.protobuf.Struct | Object structure describing the EvaluationContext used in the flag evaluation, see https://openfeature.dev/docs/reference/concepts/evaluation-context |
ResolveFloatResponse
Response body for float flag evaluation. used by the ResolveFloat rpc.
| Field | Type | Label | Description |
|---|---|---|---|
| value | double | The response value of the float flag evaluation, will be empty in the case of error. | |
| reason | string | The reason for the given return value, see https://openfeature.dev/docs/specification/types#resolution-details | |
| variant | string | The variant name of the returned flag value. | |
| metadata | google.protobuf.Struct | Metadata for this evaluation |
ResolveIntRequest
Request body for int flag evaluation, used by the ResolveInt rpc.
| Field | Type | Label | Description |
|---|---|---|---|
| flag_key | string | Flag key of the requested flag. | |
| context | google.protobuf.Struct | Object structure describing the EvaluationContext used in the flag evaluation, see https://openfeature.dev/docs/reference/concepts/evaluation-context |
ResolveIntResponse
Response body for int flag evaluation. used by the ResolveInt rpc.
| Field | Type | Label | Description |
|---|---|---|---|
| value | int64 | The response value of the int flag evaluation, will be unset in the case of error. | |
| reason | string | The reason for the given return value, see https://openfeature.dev/docs/specification/types#resolution-details | |
| variant | string | The variant name of the returned flag value. | |
| metadata | google.protobuf.Struct | Metadata for this evaluation |
ResolveObjectRequest
Request body for object flag evaluation, used by the ResolveObject rpc.
| Field | Type | Label | Description |
|---|---|---|---|
| flag_key | string | Flag key of the requested flag. | |
| context | google.protobuf.Struct | Object structure describing the EvaluationContext used in the flag evaluation, see https://openfeature.dev/docs/reference/concepts/evaluation-context |
ResolveObjectResponse
Response body for object flag evaluation. used by the ResolveObject rpc.
| Field | Type | Label | Description |
|---|---|---|---|
| value | google.protobuf.Struct | The response value of the object flag evaluation, will be unset in the case of error. |
NOTE: This structure will need to be decoded from google/protobuf/struct.proto before it is returned to the SDK | | reason | string | | The reason for the given return value, see https://openfeature.dev/docs/specification/types#resolution-details | | variant | string | | The variant name of the returned flag value. | | metadata | google.protobuf.Struct | | Metadata for this evaluation |
ResolveStringRequest
Request body for string flag evaluation, used by the ResolveString rpc.
| Field | Type | Label | Description |
|---|---|---|---|
| flag_key | string | Flag key of the requested flag. | |
| context | google.protobuf.Struct | Object structure describing the EvaluationContext used in the flag evaluation, see https://openfeature.dev/docs/reference/concepts/evaluation-context |
ResolveStringResponse
Response body for string flag evaluation. used by the ResolveString rpc.
| Field | Type | Label | Description |
|---|---|---|---|
| value | string | The response value of the string flag evaluation, will be unset in the case of error. | |
| reason | string | The reason for the given return value, see https://openfeature.dev/docs/specification/types#resolution-details | |
| variant | string | The variant name of the returned flag value. | |
| metadata | google.protobuf.Struct | Metadata for this evaluation |
Service
Service defines the exposed rpcs of flagd
| Method Name | Request Type | Response Type | Description |
|---|---|---|---|
| ResolveAll | ResolveAllRequest | ResolveAllResponse | |
| ResolveBoolean | ResolveBooleanRequest | ResolveBooleanResponse | |
| ResolveString | ResolveStringRequest | ResolveStringResponse | |
| ResolveFloat | ResolveFloatRequest | ResolveFloatResponse | |
| ResolveInt | ResolveIntRequest | ResolveIntResponse | |
| ResolveObject | ResolveObjectRequest | ResolveObjectResponse | |
| EventStream | EventStreamRequest | EventStreamResponse stream |
flagd/sync/v1/sync.proto
Flag definition sync API
This proto defines a simple API to synchronize a feature flag definition. It supports establishing a stream for getting notifications about changes in a flag definition.
FetchAllFlagsRequest
FetchAllFlagsRequest is the request to fetch all flags. Clients send this request as the client in order to resync their internal state
| Field | Type | Label | Description |
|---|---|---|---|
| provider_id | string | Optional: A unique identifier for clients initiating the request. The server implementations may utilize this identifier to uniquely identify, validate(ex:- enforce authentication/authorization) and filter flag configurations that it can expose to this request. This field is intended to be optional. However server implementations may enforce it. ex:- provider_id: flagd-weatherapp-sidecar | |
| selector | string | Deprecated. Optional: A selector for the flag configuration request. The server implementation may utilize this to select flag configurations from a collection, select the source of the flag or combine this to any desired underlying filtering mechanism. ex:- selector: 'source=database,app=weatherapp' |
Deprecated: Use the 'Flagd-Selector' header instead. Remember to reserve field number 2 if this is removed; |
FetchAllFlagsResponse
FetchAllFlagsResponse is the server response containing feature flag configurations
| Field | Type | Label | Description |
|---|---|---|---|
| flag_configuration | string | flagd feature flag configuration. Must be validated to schema - https://raw.githubusercontent.com/open-feature/flagd-schemas/main/json/flags.json |
GetMetadataRequest
GetMetadataRequest is the request for retrieving metadata from the sync service
GetMetadataResponse
GetMetadataResponse contains metadata from the sync service DEPRECATED; use flagd.sync.v1.SyncFlagsResponse.sync_context
| Field | Type | Label | Description |
|---|---|---|---|
| metadata | google.protobuf.Struct |
SyncFlagsRequest
SyncFlagsRequest is the request initiating the server-streaming rpc. Implementations of Flagd providers and Flagd itself send this request, acting as the client.
| Field | Type | Label | Description |
|---|---|---|---|
| provider_id | string | Optional: A unique identifier for flagd(grpc client) initiating the request. The server implementations may utilize this identifier to uniquely identify, validate(ex:- enforce authentication/authorization) and filter flag configurations that it can expose to this request. This field is intended to be optional. However server implementations may enforce it. ex:- provider_id: flagd-weatherapp-sidecar | |
| selector | string | Deprecated. Optional: A selector for the flag configuration request. The server implementation may utilize this to select flag configurations from a collection, select the source of the flag or combine this to any desired underlying filtering mechanism. ex:- selector: 'source=database,app=weatherapp' |
Deprecated: Use the 'Flagd-Selector' header instead. Remember to reserve field number 2 if this is removed; |
SyncFlagsResponse
SyncFlagsResponse is the server response containing feature flag configurations and the state
| Field | Type | Label | Description |
|---|---|---|---|
| flag_configuration | string | flagd feature flag configuration. Must be validated to schema - https://raw.githubusercontent.com/open-feature/flagd-schemas/main/json/flags.json | |
| sync_context | google.protobuf.Struct | optional | Static context to be included in in-process evaluations (optional). |
FlagSyncService
FlagService implements a server streaming to provide realtime flag configurations
| Method Name | Request Type | Response Type | Description |
|---|---|---|---|
| SyncFlags | SyncFlagsRequest | SyncFlagsResponse stream | |
| FetchAllFlags | FetchAllFlagsRequest | FetchAllFlagsResponse | |
| GetMetadata | GetMetadataRequest | GetMetadataResponse |
Scalar Value Types
| .proto Type | Notes | C++ | Java | Python | Go | C# | PHP | Ruby |
|---|---|---|---|---|---|---|---|---|
| double | double | double | float | float64 | double | float | Float | |
| float | float | float | float | float32 | float | float | Float | |
| int32 | Uses variable-length encoding. Inefficient for encoding negative numbers – if your field is likely to have negative values, use sint32 instead. | int32 | int | int | int32 | int | integer | Bignum or Fixnum (as required) |
| int64 | Uses variable-length encoding. Inefficient for encoding negative numbers – if your field is likely to have negative values, use sint64 instead. | int64 | long | int/long | int64 | long | integer/string | Bignum |
| uint32 | Uses variable-length encoding. | uint32 | int | int/long | uint32 | uint | integer | Bignum or Fixnum (as required) |
| uint64 | Uses variable-length encoding. | uint64 | long | int/long | uint64 | ulong | integer/string | Bignum or Fixnum (as required) |
| sint32 | Uses variable-length encoding. Signed int value. These more efficiently encode negative numbers than regular int32s. | int32 | int | int | int32 | int | integer | Bignum or Fixnum (as required) |
| sint64 | Uses variable-length encoding. Signed int value. These more efficiently encode negative numbers than regular int64s. | int64 | long | int/long | int64 | long | integer/string | Bignum |
| fixed32 | Always four bytes. More efficient than uint32 if values are often greater than . | uint32 | int | int | uint32 | uint | integer | Bignum or Fixnum (as required) |
| fixed64 | Always eight bytes. More efficient than uint64 if values are often greater than . | uint64 | long | int/long | uint64 | ulong | integer/string | Bignum |
| sfixed32 | Always four bytes. | int32 | int | int | int32 | int | integer | Bignum or Fixnum (as required) |
| sfixed64 | Always eight bytes. | int64 | long | int/long | int64 | long | integer/string | Bignum |
| bool | bool | boolean | boolean | bool | bool | boolean | TrueClass/FalseClass | |
| string | A string must always contain UTF-8 encoded or 7-bit ASCII text. | string | String | str/unicode | string | string | string | String (UTF-8) |
| bytes | May contain any arbitrary sequence of bytes. | string | ByteString | str | []byte | ByteString | string | String (ASCII-8BIT) |