@idem0/sdk

Drop-in idempotency for LLM API calls. Get exactly-once semantics for @anthropic-ai/sdk and openai — without changing how you call them.

idem0 is a lightweight proxy in front of your LLM provider. This SDK is a tiny config producer (not a client wrapper): you spread its output into the provider SDK you already use, and add one header per call. Your provider token never leaves your process — idem0 is BYOK and never sees it.

Install

npm i @idem0/sdk

Keep using your provider's official SDK — idem0 sits alongside it.

Quick start

Anthropic

import Anthropic from "@anthropic-ai/sdk";
import { idem0, idempotencyKey } from "@idem0/sdk";

const client = new Anthropic({
  apiKey: process.env.ANTHROPIC_API_KEY, // your token — BYOK, never seen by idem0
  ...idem0({ idem0Key: process.env.IDEM0_KEY, provider: "anthropic" }),
});

const message = await client.messages.create(
  { model: "claude-haiku-4-5", max_tokens: 1024, messages: [{ role: "user", content: "Hello" }] },
  { headers: idempotencyKey("job-42") }, // stable, caller-owned key → exactly-once
);

OpenAI

import OpenAI from "openai";
import { idem0, idempotencyKey } from "@idem0/sdk";

const client = new OpenAI({
  apiKey: process.env.OPENAI_API_KEY, // your token — BYOK, never seen by idem0
  ...idem0({ idem0Key: process.env.IDEM0_KEY, provider: "openai" }),
});

const completion = await client.chat.completions.create(
  { model: "gpt-5-nano", messages: [{ role: "user", content: "Hello" }] },
  { headers: idempotencyKey("job-42") },
);

Retry a request with the same Idempotency-Key and you get the original result back — instead of running, and being billed for, the call twice.

API

The entire surface is two pure functions.

idem0({ idem0Key, provider, endpoint? })

Client-level config to spread once into the provider SDK constructor. Returns { baseURL, defaultHeaders }.

Option	Required	Description
idem0Key	yes	Your idem0 client key, sent as x-idem0-key. Not your provider token.
provider	yes	"anthropic" or "openai" — selects the upstream route.
endpoint	no	Defaults to the hosted proxy (https://api.idem0.dev). Set it only if you self-host idem0.

idempotencyKey(key)

The per-call header. Returns { "Idempotency-Key": key } — drop it into a request's headers. The key is caller-owned and passed through verbatim (idem0 never generates it): use a stable id tied to your unit of work (a job id, an order id) so a retry maps to the same operation.

BYOK — your provider token stays yours

idem0 only ever handles the x-idem0-key. Your provider apiKey rides in the provider SDK's own Authorization / x-api-key header, untouched — idem0 never accepts, stores, or logs it.

Self-hosting

Running your own idem0 proxy? Pass endpoint — a bare host, no path and no /v1 (the SDK appends the provider-aware path):

idem0({ endpoint: "https://idem0.internal.acme.com", idem0Key: "…", provider: "anthropic" });

---

Part of idem0. Released under the MIT License.