diff --git a/server/src/world.rs b/server/src/world.rs
index 6adb8e2..d995d69 100644
--- a/server/src/world.rs
+++ b/server/src/world.rs
@@ -1,10 +1,18 @@
 //! `world.proto`
 
+pub mod error;
+pub mod grpc;
+mod r#impl;
+
+use std::sync::Arc;
+
 use futures::future::BoxFuture;
 use serde::{Deserialize, Serialize};
 
 use crate::prelude::IntoStatus;
 
+pub use error::Error;
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Deserialize, Serialize)]
 pub struct Size {
     pub width: u32,
@@ -78,5 +86,17 @@ pub trait ProvideWorldService: Send + Sync + 'static {
         self.world_service().check_coordinate(ctx, req)
     }
 
-    // TODO: build_server(this: Arc<Self>) -> WorldServiceServer<...>
+    fn build_server(this: Arc<Self>) -> WorldServiceServer<Self>
+    where
+        Self: Sized,
+    {
+        let service = grpc::ServiceImpl::new(this);
+        WorldServiceServer::new(service)
+    }
 }
+
+#[derive(Debug, Clone, Copy)]
+pub struct WorldServiceImpl;
+
+pub type WorldServiceServer<State> =
+    schema::world::world_service_server::WorldServiceServer<grpc::ServiceImpl<State>>;
diff --git a/server/src/world/error.rs b/server/src/world/error.rs
new file mode 100644
index 0000000..7d47827
--- /dev/null
+++ b/server/src/world/error.rs
@@ -0,0 +1,11 @@
+/// infallible
+#[derive(Debug, Clone, thiserror::Error)]
+pub enum Error {}
+
+impl From<Error> for tonic::Status {
+    fn from(value: Error) -> Self {
+        match value {}
+    }
+}
+
+pub type Result<T, E = Error> = std::result::Result<T, E>;
diff --git a/server/src/world/grpc.rs b/server/src/world/grpc.rs
new file mode 100644
index 0000000..203072b
--- /dev/null
+++ b/server/src/world/grpc.rs
@@ -0,0 +1,84 @@
+use std::sync::Arc;
+
+use schema::world as schema;
+
+use crate::prelude::IntoStatus;
+
+// MARK: type conversions
+
+impl From<super::Coordinate> for schema::Coordinate {
+    fn from(value: super::Coordinate) -> Self {
+        let super::Coordinate { x, y } = value;
+        Self { x, y }
+    }
+}
+
+impl From<schema::Coordinate> for super::Coordinate {
+    fn from(value: schema::Coordinate) -> Self {
+        let schema::Coordinate { x, y } = value;
+        Self { x, y }
+    }
+}
+
+impl From<super::Size> for schema::Size {
+    fn from(value: super::Size) -> Self {
+        let super::Size { width, height } = value;
+        Self { width, height }
+    }
+}
+
+impl From<schema::Size> for super::Size {
+    fn from(value: schema::Size) -> Self {
+        let schema::Size { width, height } = value;
+        Self { width, height }
+    }
+}
+
+// MARK: ServiceImpl
+
+pub struct ServiceImpl<State> {
+    state: Arc<State>,
+}
+
+impl<State> Clone for ServiceImpl<State>
+where
+    State: super::ProvideWorldService,
+{
+    fn clone(&self) -> Self {
+        Self {
+            state: Arc::clone(&self.state),
+        }
+    }
+}
+
+impl<State> ServiceImpl<State>
+where
+    State: super::ProvideWorldService,
+{
+    pub(super) fn new(state: Arc<State>) -> Self {
+        Self { state }
+    }
+}
+
+#[async_trait::async_trait]
+impl<State> schema::world_service_server::WorldService for ServiceImpl<State>
+where
+    State: super::ProvideWorldService,
+{
+    async fn get_world(
+        &self,
+        request: tonic::Request<schema::GetWorldRequest>,
+    ) -> tonic::Result<tonic::Response<schema::GetWorldResponse>> {
+        let (_, _, schema::GetWorldRequest {}) = request.into_parts();
+        let req = super::GetWorldSize {};
+        let size = self
+            .state
+            .get_world_size(req)
+            .await
+            .map_err(IntoStatus::into_status)?
+            .into();
+        let world = schema::World { size: Some(size) };
+        let res = schema::GetWorldResponse { world: Some(world) };
+        Ok(tonic::Response::new(res))
+    }
+}
diff --git a/server/src/world/impl.rs b/server/src/world/impl.rs
new file mode 100644
index 0000000..a539dc5
--- /dev/null
+++ b/server/src/world/impl.rs
@@ -0,0 +1,34 @@
+use futures::{future, FutureExt};
+
+impl<Context> super::WorldService<Context> for super::WorldServiceImpl
+where
+    Context: super::WorldSizeStore,
+{
+    type Error = super::Error;
+
+    fn get_world_size<'a>(
+        &'a self,
+        ctx: &'a Context,
+        req: super::GetWorldSize,
+    ) -> future::BoxFuture<'a, Result<super::Size, Self::Error>> {
+        let super::GetWorldSize {} = req;
+        let size = ctx.world_size();
+        let fut = future::ready(Ok(size));
+        fut.boxed()
+    }
+
+    fn check_coordinate<'a>(
+        &'a self,
+        ctx: &'a Context,
+        req: super::CheckCoordinate,
+    ) -> future::BoxFuture<'a, Result<super::CheckCoordinateAnswer, Self::Error>> {
+        let size = ctx.world_size();
+        let super::CheckCoordinate { coordinate } = req;
+        let res = if coordinate.x < size.width && coordinate.y < size.height {
+            super::CheckCoordinateAnswer::Valid(coordinate)
+        } else {
+            super::CheckCoordinateAnswer::Invalid
+        };
+        future::ready(Ok(res)).boxed()
+    }
+}