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By James Newton-King

Tooling is available for gRPC that allows developers to test services without building client apps:

Postman is an API platform with an interactive UI for calling APIs. Postman can run in the browser or be downloaded and run locally. Postman supports calling gRPC services.

gRPCurl is an open-source command-line tool that provides interaction with gRPC services.

gRPCui builds on top of gRPCurl and adds an open-source interactive web UI for gRPC.

This article discusses how to:

Set up gRPC server reflection with a gRPC ASP.NET Core app.

Interact with gRPC using test tools:

Call gRPC services in Postman.

Discover and test gRPC services with grpcurl .

Interact with gRPC services via a browser using grpcui .

To learn how to unit test gRPC services, see Test gRPC services in ASP.NET Core .

Set up gRPC reflection

Tooling must know the Protobuf contract of services before it can call them. There are two ways to do this:

Set up gRPC reflection on the server. Tools, such as gRPCurl and Postman, use reflection to automatically discover service contracts.

Add .proto files to the tool manually.

It's easier to use gRPC reflection. gRPC reflection adds a new gRPC service to the app that clients can call to discover services.

gRPC ASP.NET Core has built-in support for gRPC reflection with the Grpc.AspNetCore.Server.Reflection package. To configure reflection in an app:

Add a Grpc.AspNetCore.Server.Reflection package reference.

Register reflection in Program.cs :

AddGrpcReflection to register services that enable reflection.

MapGrpcReflectionService to add a reflection service endpoint.

builder.Services.AddGrpc();
builder.Services.AddGrpcReflection();
var app = builder.Build();
app.MapGrpcService<GreeterService>();
IWebHostEnvironment env = app.Environment;
if (env.IsDevelopment())
    app.MapGrpcReflectionService();
When gRPC reflection is set up:
A gRPC reflection service is added to the server app.
Client apps that support gRPC reflection can call the reflection service to discover services hosted by the server.
gRPC services are still called from the client. Reflection only enables service discovery and doesn't bypass server-side security. Endpoints protected by authentication and authorization require the caller to pass credentials for the endpoint to be called successfully.
Postman
Postman is an API platform. It supports calling gRPC services with an interactive UI, among its many features.
To download and install Postman, see the Download Postman page.
Use Postman
Postman has an interactive UI for calling gRPC services. To call a gRPC service using Postman:
Select the New button and choose gRPC Request.
Enter the gRPC server's hostname and port in the server URL. For example, localhost:5000. Don't include the http or https scheme in the URL. If the server uses Transport Layer Security (TLS), select the padlock next to the server URL to enable TLS in Postman.
Navigate to the Service definition section, then select server reflection or import the app's proto file. When complete, the dropdown list next to the server URL textbox has a list of gRPC methods available.
To call a gRPC method, select it in the dropdown, select Generate Example Message, then select Invoke to send the gRPC call to the server.
A short video is also available that walks through using Postman with gRPC.
gRPCurl
gRPCurl is a command-line tool created by the gRPC community. Its features include:
Calling gRPC services, including streaming services.
Service discovery using gRPC reflection.
Listing and describing gRPC services.
Works with secure (TLS) and insecure (plain-text) servers.
For information about downloading and installing grpcurl, see the gRPCurl GitHub homepage.
Use grpcurl
The -help argument explains grpcurl command-line options:
$ grpcurl -help
Discover services
Use the describe verb to view the services defined by the server. Specify <port> as the localhost port number of the gRPC server. The port number is randomly assigned when the project is created and set in Properties/launchSettings.json:
$ grpcurl localhost:<port> describe
greet.Greeter is a service:
service Greeter {
  rpc SayHello ( .greet.HelloRequest ) returns ( .greet.HelloReply );
  rpc SayHellos ( .greet.HelloRequest ) returns ( stream .greet.HelloReply );
grpc.reflection.v1alpha.ServerReflection is a service:
service ServerReflection {
  rpc ServerReflectionInfo ( stream .grpc.reflection.v1alpha.ServerReflectionRequest ) returns ( stream .grpc.reflection.v1alpha.ServerReflectionResponse );
The preceding example:
Runs the describe verb on server localhost:<port>. Where <port> is randomly assigned when the gRPC server project is created and set in Properties/launchSettings.json
Prints services and methods returned by gRPC reflection.
Greeter is a service implemented by the app.
ServerReflection is the service added by the Grpc.AspNetCore.Server.Reflection package.
Combine describe with a service, method, or message name to view its detail:
$ grpcurl localhost:<port> describe greet.HelloRequest
greet.HelloRequest is a message:
message HelloRequest {
  string name = 1;
Call gRPC services
Call a gRPC service by specifying a service and method name along with a JSON argument that represents the request message. The JSON is converted into Protobuf and sent to the service.
$ grpcurl -d '{ \"name\": \"World\" }' localhost:<port> greet.Greeter/SayHello
  "message": "Hello World"
In the preceding example:
The -d argument specifies a request message with JSON. This argument must come before the server address and method name.
Calls the SayHello method on the greeter.Greeter service.
Prints the response message as JSON.
Where <port> is randomly assigned when the gRPC server project is created and set in Properties/launchSettings.json
The preceding example uses \ to escape the " character. Escaping " is required in a PowerShell console but must not be used in some consoles. For example, the previous command for a macOS console:
$ grpcurl -d '{ "name": "World" }' localhost:<port> greet.Greeter/SayHello
  "message": "Hello World"
gRPCui
gRPCui is an interactive web UI for gRPC. gRPCui builds on top of gRPCurl. gRPCui offers a GUI for discovering and testing gRPC services, similar to HTTP tools such as Postman or Swagger UI.
For information about downloading and installing grpcui, see the gRPCui GitHub homepage.
Using grpcui
Run grpcui with the server address to interact with as an argument:
$ grpcui localhost:<port>
gRPC Web UI available at http://127.0.0.1:55038/
In the preceding example, specify <port> as the localhost port number of the gRPC server. The port number is randomly assigned when the project is created and set in Properties/launchSettings.json
The tool launches a browser window with the interactive web UI. gRPC services are automatically discovered using gRPC reflection.
Additional resources
Postman homepage
gRPCurl GitHub homepage
gRPCui GitHub homepage
Grpc.AspNetCore.Server.Reflection
Test gRPC services in ASP.NET Core
Mock gRPC client in tests
Tooling is available for gRPC that allows developers to test services without building client apps:
Postman is an API platform with an interactive UI for calling APIs. Postman can run in the browser or be downloaded and run locally. Postman supports calling gRPC services.
gRPCurl is an open-source command-line tool that provides interaction with gRPC services.
gRPCui builds on top of gRPCurl and adds an open-source interactive web UI for gRPC.
This article discusses how to:
Set up gRPC server reflection with a gRPC ASP.NET Core app.
Interact with gRPC using test tools:
Call gRPC services in Postman.
Discover and test gRPC services with grpcurl.
Interact with gRPC services via a browser using grpcui.
To learn how to unit test gRPC services, see Test gRPC services in ASP.NET Core.
Set up gRPC reflection
Tooling must know the Protobuf contract of services before it can call them. There are two ways to do this:
Set up gRPC reflection on the server. Tools, such as gRPCurl and Postman, use reflection to automatically discover service contracts.
Add .proto files to the tool manually.
It's easier to use gRPC reflection. gRPC reflection adds a new gRPC service to the app that clients can call to discover services.
gRPC ASP.NET Core has built-in support for gRPC reflection with the Grpc.AspNetCore.Server.Reflection package. To configure reflection in an app:
Add a Grpc.AspNetCore.Server.Reflection package reference.
Register reflection in Startup.cs:
AddGrpcReflection to register services that enable reflection.
MapGrpcReflectionService to add a reflection service endpoint.
public void ConfigureServices(IServiceCollection services)
    services.AddGrpc();
    services.AddGrpcReflection();
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    app.UseRouting();
    app.UseEndpoints(endpoints =>
        endpoints.MapGrpcService<GreeterService>();
        if (env.IsDevelopment())
            endpoints.MapGrpcReflectionService();
When gRPC reflection is set up:
A gRPC reflection service is added to the server app.
Client apps that support gRPC reflection can call the reflection service to discover services hosted by the server.
gRPC services are still called from the client. Reflection only enables service discovery and doesn't bypass server-side security. Endpoints protected by authentication and authorization require the caller to pass credentials for the endpoint to be called successfully.
Postman
Postman is an API platform. It supports calling gRPC services with an interactive UI, among its many features.
To download and install Postman, see the Download Postman page.
Use Postman
Postman has an interactive UI for calling gRPC services. To call a gRPC service using Postman:
Select the New button and choose gRPC Request.
Enter the gRPC server's hostname and port in the server URL. For example, localhost:5000. Don't include the http or https scheme in the URL. If the server uses Transport Layer Security (TLS), select the padlock next to the server URL to enable TLS in Postman.
Navigate to the Service definition section, then select server reflection or import the app's proto file. When complete, the dropdown list next to the server URL textbox has a list of gRPC methods available.
To call a gRPC method, select it in the dropdown, select Generate Example Message, then select Invoke to send the gRPC call to the server.
A short video is also available that walks through using Postman with gRPC.
gRPCurl
gRPCurl is a command-line tool created by the gRPC community. Its features include:
Calling gRPC services, including streaming services.
Service discovery using gRPC reflection.
Listing and describing gRPC services.
Works with secure (TLS) and insecure (plain-text) servers.
For information about downloading and installing grpcurl, see the gRPCurl GitHub homepage.
Use grpcurl
The -help argument explains grpcurl command-line options:
$ grpcurl -help
Discover services
Use the describe verb to view the services defined by the server:
$ grpcurl localhost:5001 describe
greet.Greeter is a service:
service Greeter {
  rpc SayHello ( .greet.HelloRequest ) returns ( .greet.HelloReply );
  rpc SayHellos ( .greet.HelloRequest ) returns ( stream .greet.HelloReply );
grpc.reflection.v1alpha.ServerReflection is a service:
service ServerReflection {
  rpc ServerReflectionInfo ( stream .grpc.reflection.v1alpha.ServerReflectionRequest ) returns ( stream .grpc.reflection.v1alpha.ServerReflectionResponse );
The preceding example:
Runs the describe verb on server localhost:5001.
Prints services and methods returned by gRPC reflection.
Greeter is a service implemented by the app.
ServerReflection is the service added by the Grpc.AspNetCore.Server.Reflection package.
Combine describe with a service, method, or message name to view its detail:
$ grpcurl localhost:5001 describe greet.HelloRequest
greet.HelloRequest is a message:
message HelloRequest {
  string name = 1;
Call gRPC services
Call a gRPC service by specifying a service and method name along with a JSON argument that represents the request message. The JSON is converted into Protobuf and sent to the service.
$ grpcurl -d '{ \"name\": \"World\" }' localhost:5001 greet.Greeter/SayHello
  "message": "Hello World"
In the preceding example:
The -d argument specifies a request message with JSON. This argument must come before the server address and method name.
Calls the SayHello method on the greeter.Greeter service.
Prints the response message as JSON.
The preceding example uses \ to escape the " character. Escaping " is required in a PowerShell console but must not be used in some consoles. For example, the previous command for a macOS console:
$ grpcurl -d '{ "name": "World" }' localhost:5001 greet.Greeter/SayHello
  "message": "Hello World"
gRPCui
gRPCui is an interactive web UI for gRPC. gRPCui builds on top of gRPCurl. gRPCui offers a GUI for discovering and testing gRPC services, similar to HTTP tools such as Postman or Swagger UI.
For information about downloading and installing grpcui, see the gRPCui GitHub homepage.
Using grpcui
Run grpcui with the server address to interact with as an argument:
$ grpcui localhost:5001
gRPC Web UI available at http://127.0.0.1:55038/
The tool launches a browser window with the interactive web UI. gRPC services are automatically discovered using gRPC reflection.
Additional resources
Postman homepage
gRPCurl GitHub homepage
gRPCui GitHub homepage
Grpc.AspNetCore.Server.Reflection
Test gRPC services in ASP.NET Core
Mock gRPC client in tests