> ## Documentation Index
> Fetch the complete documentation index at: https://docs.idem0.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Quickstart

> Make your first idempotent call, then watch the same call replay for free.

You'll install the SDK, make one call, then run the **same** call again and watch idem0 return it from cache for zero credits. That last step is the whole point — don't skip it.

<Steps>
  <Step title="Install">
    ```bash theme={null}
    npm i @idem0/sdk
    ```

    You'll also need the provider SDK you already use — `@anthropic-ai/sdk` or `openai`.
  </Step>

  <Step title="Get your key">
    Grab an idem0 key from [your dashboard](https://idem0.dev/login) and export it. This is your **idem0** key (`x-idem0-key`) — not your provider key.

    ```bash theme={null}
    export IDEM0_KEY="idem0_live_..."
    ```
  </Step>

  <Step title="Make your first call">
    Spread `idem0(...)` into the provider client once, and drop `idempotencyKey(...)` into the call. Your provider key rides in the SDK's own `apiKey`, untouched (BYOK).

    <CodeGroup>
      ```ts Anthropic theme={null}
      import Anthropic from "@anthropic-ai/sdk";
      import { idem0, idempotencyKey } from "@idem0/sdk";

      const client = new Anthropic({
        apiKey: process.env.ANTHROPIC_API_KEY,
        ...idem0({ idem0Key: process.env.IDEM0_KEY, provider: "anthropic" }),
      });

      const message = await client.messages.create(
        {
          model: "claude-haiku-4-5",
          max_tokens: 64,
          messages: [{ role: "user", content: "Say hi in one word." }],
        },
        { headers: idempotencyKey("job-42") },
      );

      console.log(message.content);
      ```

      ```ts OpenAI theme={null}
      import OpenAI from "openai";
      import { idem0, idempotencyKey } from "@idem0/sdk";

      const client = new OpenAI({
        apiKey: process.env.OPENAI_API_KEY,
        ...idem0({ idem0Key: process.env.IDEM0_KEY, provider: "openai" }),
      });

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

      console.log(completion.choices[0].message.content);
      ```
    </CodeGroup>

    `endpoint` defaults to the hosted proxy (`https://api.idem0.dev`) — you only pass it when self-hosting.
  </Step>

  <Step title="See the replay (the whole point)">
    Run the **exact same request** twice and watch the second one come back from cache. Here it is with raw `curl -i` so you can see the response headers — use an `Idempotency-Key` you haven't used yet, then run the command a **second time unchanged**:

    ```bash theme={null}
    curl -i https://api.idem0.dev/anthropic/v1/messages \
      -H "x-idem0-key: $IDEM0_KEY" \
      -H "x-api-key: $ANTHROPIC_API_KEY" \
      -H "anthropic-version: 2023-06-01" \
      -H "content-type: application/json" \
      -H "Idempotency-Key: demo-001" \
      -d '{"model":"claude-haiku-4-5","max_tokens":64,"messages":[{"role":"user","content":"Say hi in one word."}]}'
    ```

    **First call** — the model runs, you're billed one call. No replay header:

    ```http theme={null}
    HTTP/2 200
    content-type: application/json
    ```

    **Second call, same `Idempotency-Key`** — idem0 returns the stored response byte-for-byte, and bills you **nothing**:

    ```http theme={null}
    HTTP/2 200
    content-type: application/json
    idem0-idempotent-replayed: true
    ```

    That `idem0-idempotent-replayed: true` is the tell: no model ran, no credit spent. Same key, same answer. (OpenAI is identical — `POST https://api.idem0.dev/openai/v1/chat/completions` with `Authorization: Bearer $OPENAI_API_KEY`.)
  </Step>
</Steps>

## What next

<CardGroup cols={2}>
  <Card title="Concepts" icon="book" href="/concepts">
    Pick good keys and understand the 30-day replay window.
  </Card>

  <Card title="API reference" icon="code" href="/api-reference">
    The full SDK surface and HTTP contract.
  </Card>
</CardGroup>