Effect-native client

Choose the Effect client when your application already uses Effect for retries, dependencies, tracing, or error handling. Operations stay in Effect; no Promise boundary is introduced until you decide to run one.

Keep that choice in config so every regeneration uses the same client style:

import { defineConfig } from "typed-openapi";

export default defineConfig({
  input: "./openapi.yaml",
  output: "./src/api/openapi.ts",
  runtime: "effect",
  client: "effect",
  defaultFetcher: "api.client.ts",
});

Or make the same client from the command line:

pnpm add effect
pnpm exec typed-openapi ./openapi.yaml \
  --runtime effect \
  --client effect \
  --default-fetcher \
  --output src/api/openapi.ts

effect and effect3 select the Effect client by default, so --client effect is optional for those runtimes.

Run an operation

Generated methods return an Effect, not a Promise:

import { Effect } from "effect";
import { api } from "./api/api.client";
import { HttpClientError, TypedStatusError } from "./api/openapi";

const program = api.get("/pet/{petId}", { path: { petId: 7 } }).pipe(
  Effect.tap((pet) => Effect.log(`Loaded ${pet.name}`)),
);

const pet = await Effect.runPromise(program);

Handle the error channel

Status errors are TypedStatusError; transport, decoding, parsing, and validation failures are remapped to HttpClientError, which keeps the original problem in cause.

const program = api.get("/pet/{petId}", { path: { petId: 7 } }).pipe(
  Effect.catchAll((error) => {
    if (error instanceof TypedStatusError) return Effect.succeed({ kind: "status-error", error });
    if (error instanceof HttpClientError) return Effect.fail(error.cause);
    return Effect.fail(error);
  }),
);

The generated TanStack helpers automatically use Effect.runPromise when the API client is Effect-native.