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

# Prflght TypeScript SDK: Install and Use @prflght/sdk

> Install @prflght/sdk to add Prflght's transaction firewall to any TypeScript Solana agent. Call check() before sending transactions.

The `@prflght/sdk` package is the lowest-level way to integrate Prflght into your agent. You call `firewall.check()` before sending any transaction, receive attestation instructions on allow, and catch `FirewallDenyError` on deny. Every other Prflght integration is built on top of this SDK.

## Installation

<CodeGroup>
  ```bash npm theme={null}
  npm install @prflght/sdk
  ```

  ```bash bun theme={null}
  bun add @prflght/sdk
  ```
</CodeGroup>

## Initialization

Create a `Firewall` instance once at startup and reuse it for every transaction check. You need two values:

* **`apiUrl`** — the Prflght API base URL: `https://api.prflght.xyz`
* **`agentId`** — your agent's Solana wallet public key as a base58 string

```typescript theme={null}
import { Firewall, FirewallDenyError } from '@prflght/sdk'

const firewall = new Firewall({
  apiUrl: 'https://api.prflght.xyz',
  agentId: agentKeypair.publicKey.toString(),
})
```

## The check() method

Call `firewall.check()` before sending any transaction. Pass the transaction as a base64-encoded serialized `VersionedTransaction`.

On allow, `check()` returns an object with an `instructions` array — these are attestation instructions you must prepend to your transaction before submitting it on-chain.

On deny, `check()` throws a `FirewallDenyError` with a `.reason` string describing why the transaction was blocked.

<Note>
  You must prepend the returned attestation instructions to your transaction before sending. The Prflght on-chain program verifies the attestation at execution time — submitting without them will cause the transaction to fail.
</Note>

### Full example

```typescript theme={null}
import { Firewall, FirewallDenyError } from '@prflght/sdk'

const firewall = new Firewall({
  apiUrl: 'https://api.prflght.xyz',
  agentId: agentKeypair.publicKey.toString(),
})

// Before sending any transaction:
try {
  const result = await firewall.check(txBase64)
  // result.instructions = attestation ixs to prepend to your tx
  const finalTx = buildTxWithIxs([...result.instructions, ...yourIxs])
  await sendAndConfirm(finalTx)
} catch (err) {
  if (err instanceof FirewallDenyError) {
    console.error('Blocked:', err.reason) // e.g. "notional exceeds policy limit"
  }
}
```

<Tip>
  To serialize a `VersionedTransaction` to base64, use:

  ```typescript theme={null}
  const txBase64 = Buffer.from(tx.serialize()).toString('base64')
  ```

  Make sure you serialize the transaction after signing but before calling `check()`.
</Tip>

## Error handling

`FirewallDenyError` is thrown whenever Prflght blocks a transaction. Catch it separately from other errors so you can handle policy denials without masking unexpected failures.

| Property     | Type     | Description                                                  |
| ------------ | -------- | ------------------------------------------------------------ |
| `err.reason` | `string` | Human-readable explanation of why the transaction was denied |

Common reason strings include:

* `"notional exceeds policy limit"` — the transaction value exceeds your agent's configured spending cap
* `"program not in allowlist"` — the transaction calls a Solana program your policy does not permit
* `"slippage exceeds policy limit"` — the swap slippage tolerance is above your configured threshold
* `"protocol health check failed"` — the DeFi protocol involved has TVL below your minimum health threshold

```typescript theme={null}
try {
  const result = await firewall.check(txBase64)
  // proceed
} catch (err) {
  if (err instanceof FirewallDenyError) {
    // Handle policy denial — log, alert, or skip the transaction
    console.error('Transaction blocked by Prflght:', err.reason)
  } else {
    // Re-throw unexpected errors
    throw err
  }
}
```