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Service Client

The ServiceClient class available within the @eventual/client package provides a generic client for interacting with your Service's Commands over HTTP. It can be easily integrated into any consuming application, for example a frontend web application or even another service without any code generation.

Create a ServiceClient

import { ServiceClient } from "@eventual/client";

const client = new ServiceClient({
serviceUrl: "your-url",

Provide the type of your Service

Before you can safely call the commands, you need to provide the types of your backend service.

import type * as MyService from "@my/service";

const client = new ServiceClient<typeof MyService>({
serviceUrl: "your-url",

// type-safe interaction with commands (no code gen)
await client.myCommandName({
key: "value",

Make sure to use a type-only import when importing your backend code. If you don't, then your entire backend code will be imported into the consuming application which is unlikely to be what you want.

import type * as MyService from "@my/service";
// ^ make sure to specify import type


By default, the ServiceClient does not attempt to attach authorization headers. To do this on your own, pass in a beforeRequest callback to modify the request prior to execution.

For example, to inject a JWT token from AWS Cognito session:

new ServiceClient<typeof MyService>({
serviceUrl: process.env.SERVICE_URL!,
beforeRequest: async (request) => {
if (session) {
request.headers ??= {};
request.headers.Authorization = `Basic ${session
return request;

AWS IAM Authorization

Use the AWSServiceClient to authorize with AWS IAM Roles or IAM Users. It will by default attempt to detect credentials from the environment variables.

import { AWSServiceClient } from "@eventual/aws-client";

import type * as MyService from "@my/service";

const client = new AWSServiceClient<typeof MyService>({
serviceUrl: "your-url",

You can also provide an AWS Credentials Provider from the AWS SDK v3.

import { fromEnv } from "@aws-sdk/credential-providers";

const client = new AWSServiceClient<typeof MyService>({
serviceUrl: "your-url",
credentials: fromEnv(),