# Quickstart

By the end of this page, you'll have a working integration that reads a tenant's financial state in natural language, proposes a payment, and pulls a verifiable receipt for what happened. Five minutes

### 1. Install

```bash
npm install @brain/sdk
```

### 2. Get a key

Sign up at [console.brain.dev](https://console.brain.dev), create a tenant, and copy your sandbox API key (`brain_sk_test_...`).

```bash
# .env
BRAIN_API_KEY=brain_sk_test_...
```

{% hint style="info" %}
Sandbox uses test credentials and Base Sepolia for on-chain anchoring. No real money moves. Production keys (`brain_sk_live_...`) work the same way against `console.brain.fi`.
{% endhint %}

### 3. Build

```typescript
import { Brain } from "@brain/sdk";

const brain = new Brain({ apiKey: process.env.BRAIN_API_KEY });

// Connect a sandbox source (Plaid test data lands in seconds).
await brain.sources.connect("acme", { type: "plaid", credentials: { sandbox: true } });

// Ask the tenant's financial brain a question.
const answer = await brain.ask("acme", "What did we spend on AWS last month?");
console.log(answer.text);
console.log(answer.citations);

// Propose a payment.
const action = await brain.pay("acme", { invoiceId: "inv_8231" });
console.log(action.status); // "auto" | "needs_approval" | "rejected"

// If it needs approval, approve it (in real apps, a human in your UI does this).
if (action.status === "needs_approval") {
  await brain.approve(action.id, { as: "user_cfo" });
}

// Pull a verifiable receipt.
const proof = await brain.proof(action.id);
console.log(proof.txHash);     // on-chain anchor on Base
console.log(proof.merklePath); // verifiable without trusting Brain
```

That's it. You just touched all five capabilities of Brain through one client.

### 4. What you just built

| Line                    | What Brain did under the hood                                                                                 |
| ----------------------- | ------------------------------------------------------------------------------------------------------------- |
| `brain.sources.connect` | Ingested 90 days of Plaid sandbox data, built a structured record per transaction, indexed it for retrieval   |
| `brain.ask`             | Routed your question to a memory graph, retrieved relevant facts with citations, answered in natural language |
| `brain.pay`             | Evaluated the action against the tenant's signed policy, returned an immediate decision                       |
| `brain.approve`         | Recorded a typed signature against the policy's required approvers                                            |
| `brain.proof`           | Pulled a Merkle proof from a tamper-evident log anchored on Base L2                                           |

You'll meet each of these underneath as you go deeper. For now, they're just five methods on one client.

### Where to go next

<table data-view="cards"><thead><tr><th></th><th></th><th data-type="content-ref"></th><th data-hidden data-card-target data-type="content-ref"></th></tr></thead><tbody><tr><td><strong>🛠 Build</strong></td><td>Task-shaped guides. Read a tenant's full financial picture, give an agent a spending limit, audit every action.</td><td><a href="/pages/sMrrX25ZQX2RkFLnKr3L">/pages/sMrrX25ZQX2RkFLnKr3L</a></td><td></td></tr><tr><td><strong>📐 Concepts</strong></td><td>The mental model in five minutes.</td><td><a href="/pages/xLV8vzuuJnAyV80xBwME">/pages/xLV8vzuuJnAyV80xBwME</a></td><td></td></tr><tr><td><strong>📦 Protocol</strong></td><td>The deep stack: six layers, smart contracts, on-chain anchoring.</td><td><a href="/pages/DGQRMedmp626EiwDlcTi">/pages/DGQRMedmp626EiwDlcTi</a></td><td></td></tr></tbody></table>

### Stuck?

| Problem             | Fix                                                                                       |
| ------------------- | ----------------------------------------------------------------------------------------- |
| `AUTH_INVALID_KEY`  | Check `.env`. Sandbox keys start with `brain_sk_test_`, production with `brain_sk_live_`. |
| `TENANT_NOT_FOUND`  | Create a tenant in the Console first. Tenant IDs are case-sensitive.                      |
| `SOURCE_RATE_LIMIT` | Sandbox limits are 60 rpm. Wait and retry.                                                |

[**→ Full error reference**](/resources/errors.md)


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.brain.fi/introduction/quickstart.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.