g­RPC API

Rerun components talk to each other over gRPC. The protocol is defined by the .proto files in crates/store/re_protos/proto, and every Rerun server also describes itself through gRPC server reflection.

Servers and services

MessageProxyService carries logged data between SDKs and Viewers. ViewerControlService drives a running Viewer, and is what the MCP server uses. RerunCloudService is the catalog and query API that rerun.catalog.CatalogClient speaks. It is served by two different catalogs:

• The Viewer serves its internal catalog: the recordings currently loaded in that Viewer. It only accepts connections from the local machine, like ViewerControlService.
• rerun server serves a catalog of the .rrd files and tables it was started with, for any client that can reach it.

Server reflection

Reflection lets generic gRPC tooling discover the services and message types of a live server, without access to the .proto files. Both the v1 and the v1alpha reflection protocols are served.

Using grpcurl:

# Which services does this address speak?
grpcurl -plaintext 127.0.0.1:9876 list

# Describe a service, or a message type:
grpcurl -plaintext 127.0.0.1:9876 describe rerun.cloud.v1alpha1.RerunCloudService
grpcurl -plaintext 127.0.0.1:9876 describe rerun.cloud.v1alpha1.FindEntriesRequest

# Call a method:
grpcurl -plaintext -d '{}' 127.0.0.1:9876 rerun.cloud.v1alpha1.RerunCloudService/FindEntries

list names only the services the address serves. describe knows the whole Rerun protocol, including message types of services the address does not serve.