# Envoy Gateway Extension Server

**Canonical:** https://apis.io/apis/envoy-gateway/envoy-gateway-extension-server/  
**Provider:** Envoy Gateway — https://apis.io/providers/envoy-gateway/  
**Base URL:** https://{extension-server-host}:{port}  
**Documentation:** https://gateway.envoyproxy.io/docs/tasks/extensibility/extension-server/

Envoy Gateway Extension Server is one of 3 APIs that [Envoy Gateway](https://apis.io/providers/envoy-gateway/) publishes on the [APIs.io](https://apis.io/) network. Tagged areas include gRPC, Extensibility, and xDS. The published artifact set on APIs.io includes API documentation.

A gRPC contract an operator implements to extend Envoy Gateway. Envoy Gateway is the client: during xDS translation it calls the six EnvoyGatewayExtension RPCs — PostRouteModify, PostVirtualHostModify, PostHTTPListenerModify, PostClusterModify, PostEndpointsModify and PostTranslateModify — so the extension can modify generated Envoy routes, virtual hosts, listeners, clusters, endpoints and the full translated output before it reaches the proxies. Messages are typed against Envoy's own v3 config protos, pinned to buf.build/envoyproxy/envoy:v1.33.0.

## Machine-readable artifacts (3)

- **Documentation** — https://gateway.envoyproxy.io/docs/tasks/extensibility/extension-server/
- **Protobuf** — https://raw.githubusercontent.com/api-evangelist/envoy-gateway/refs/heads/main/grpc/envoy-gateway-extension-service.proto
- **Protobuf** — https://raw.githubusercontent.com/api-evangelist/envoy-gateway/refs/heads/main/grpc/envoy-gateway-extension-context.proto

## Other Envoy Gateway APIs (2)

- [Envoy Gateway](https://apis.io/apis/envoy-gateway/envoy-gateway/)
- [Envoy Gateway Remote Infrastructure Provider](https://apis.io/apis/envoy-gateway/envoy-gateway-remote-infrastructure/)

## Tags

gRPC, Extensibility, xDS

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Profiled by [API Evangelist](https://apievangelist.com) and published on [APIs.io](https://apis.io/apis/envoy-gateway/envoy-gateway-extension-server/). The API's provider profile, Kin Score and agent-readiness rating are at https://apis.io/providers/envoy-gateway/.