Supported evaluation protocols — REST, gRPC, Connect-RPC, OFREP, SSE

Protocols

Flaggr supports multiple evaluation protocols to fit any architecture. The examples below all evaluate the same flag (checkout-v2 for user-123) so you can compare protocols side by side.

REST API

The standard HTTP/JSON API for flag evaluation.

Evaluate a Flag

curl -s -X POST https://flaggr.dev/api/flags/evaluate \
  -H "Authorization: Bearer flg_abc123xxxxxxxxxxxx" \
  -H "Content-Type: application/json" \
  -d '{
    "flagKey": "checkout-v2",
    "serviceId": "web-app",
    "environment": "production",
    "context": {
      "targetingKey": "user-123",
      "email": "alice@example.com"
    },
    "defaultValue": false
  }' | jq

Response:

{
  "flagKey": "checkout-v2",
  "value": true,
  "reason": "TARGETING_MATCH",
  "variant": "enabled"
}

Connect-RPC

Type-safe RPC protocol with full protobuf support. Ideal for service-to-service communication. Requests use the Connect-Protocol-Version: 1 header.

Evaluate a Flag

curl -s -X POST https://flaggr.dev/flaggr.v1.EvaluationService/EvaluateFlag \
  -H "Authorization: Bearer flg_abc123xxxxxxxxxxxx" \
  -H "Content-Type: application/json" \
  -H "Connect-Protocol-Version: 1" \
  -d '{
    "flagKey": "checkout-v2",
    "serviceId": "web-app",
    "context": {
      "targetingKey": "user-123",
      "email": "alice@example.com"
    }
  }' | jq

gRPC-Web

Binary gRPC protocol for browser environments. Provides streaming support for real-time flag updates.

const client = await createFlaggrClient({
  mode: 'grpc-web',
  apiUrl: 'https://flaggr.dev',
  serviceId: 'my-service',
})

Streaming Updates

gRPC-Web supports server-side streaming for real-time flag changes:

const stream = client.streamFlagUpdates({
  flagKeys: ['checkout-v2', 'dark-mode'],
})
 
for await (const update of stream) {
  console.log(`Flag ${update.flagKey} changed to ${update.value}`)
}

OFREP (OpenFeature Remote Evaluation Protocol)

Standard OpenFeature remote evaluation protocol. Any OFREP-compatible client works with Flaggr without code changes.

Evaluate a Flag

curl -s -X POST https://flaggr.dev/api/ofrep/v1/evaluate/flags/checkout-v2 \
  -H "Authorization: Bearer flg_abc123xxxxxxxxxxxx" \
  -H "Content-Type: application/json" \
  -H "X-Service-Id: web-app" \
  -d '{
    "context": {
      "targetingKey": "user-123",
      "email": "alice@example.com"
    }
  }' | jq

Response follows the OFREP specification:

{
  "key": "checkout-v2",
  "value": true,
  "reason": "TARGETING_MATCH",
  "variant": "enabled",
  "metadata": {}
}

SSE (Server-Sent Events)

Real-time flag change notifications via Server-Sent Events. The connection stays open and pushes events as flags are toggled.

# SSE streams stay open — press Ctrl-C to stop
curl -N "https://flaggr.dev/api/flags/stream?serviceId=web-app" \
  -H "Authorization: Bearer flg_abc123xxxxxxxxxxxx" \
  -H "Accept: text/event-stream"

Protocol Comparison

Feature	REST	Connect	gRPC-Web	OFREP	SSE
Browser support	Yes	Yes	Yes	Yes	Yes
Server support	Yes	Yes	No	Yes	No
Streaming	No	No	Yes	No	Yes
Type safety	No	Yes	Yes	No	No
Protobuf	No	Yes	Yes	No	No
Standard	Custom	Connect	gRPC	OpenFeature	W3C

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