Paid API (x402)

Access Silverback's DeFi intelligence through micropayments.

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What is x402?

x402 is a micropayment protocol built on HTTP. When you request a paid endpoint, the server responds with HTTP 402 Payment Required along with accepted payment options. Your client signs a payment authorization, re-sends the request, and the payment settles on-chain automatically.

You only pay if you get a response. No subscriptions, no API keys, no accounts.

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How It Works

1. Request any paid endpoint

2. Receive a 402 response with payment options

3. Sign a payment authorization (tokens don't leave your wallet yet)

4. Re-send the request with the signed payment attached

5. Receive the data — payment settles on-chain in the background

The x402 SDK handles steps 2-4 automatically, so you can use it just like a normal fetch call.

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Accepted Tokens

Pay with any of these tokens on Base (Chain ID 8453):

Token	Type	Settlement Fee	Notes
$BACK	Silverback Native	0% (fee-exempt)	20% discount on all endpoints
USDC	Stablecoin	0.1%	Primary payment token
USDT	Stablecoin	0.1%
DAI	Stablecoin	0.1%
VIRTUAL	Ecosystem	0.1%	Virtuals Protocol token
WETH	Blue-chip	0.25%	Wrapped Ether
cbBTC	Blue-chip	0.25%	Coinbase Wrapped BTC

USDC payments are also accepted via the Keeta payment network.

Prices for volatile tokens (BACK, VIRTUAL, WETH, cbBTC) are calculated using live market rates, refreshed every 5 minutes.

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$BACK Payment Benefits

Paying with $BACK gives you two advantages over any other token:

• Zero settlement fees — all other tokens incur 0.1% to 0.25%

• 20% discount on every endpoint — a $0.02 endpoint costs only $0.016 in BACK

This is the cheapest way to access Silverback's intelligence services.

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Available Endpoints

Market Data ($0.001)

Endpoint	Description
Gas Price	Current Base network gas prices and estimates
Trending Tokens	Trending tokens on Base
Top Coins	Top coins by market cap with Silverback intelligence signals
Top Pools	Top liquidity pools ranked by APR
Top Protocols	Top DeFi protocols by TVL
Token Metadata	Detailed token information, links, and stats

Agent Intelligence ($0.001 - $0.002)

Endpoint	Price	Description
Agent Reputation	$0.001	On-chain agent reputation scores (ERC-8004)
Agent Discover	$0.002	Discover registered AI agents on Base

Trading Tools ($0.002 - $0.05)

Endpoint	Price	Description
Swap Quote	$0.002	DEX swap quotes via 0x Protocol aggregation
Pool Analysis	$0.005	Pool reserves, TVL, fees, and risk analysis
Correlation Matrix	$0.005	Multi-token price correlations (30-day)
Token Audit	$0.01	Smart contract security audit (honeypot, taxes, ownership)
Whale Moves	$0.01	Large holder movement tracking
Technical Analysis	$0.02	RSI, EMA, Bollinger Bands, and chart patterns
DeFi Yield	$0.02	DeFi yield opportunities across Base protocols
Arbitrage Scanner	$0.02	Cross-DEX price spread detection
Swap Execution	$0.05	Execute a DEX swap

Advanced ($0.10)

Endpoint	Price	Description
Backtest	$0.10	Historical trading strategy backtesting

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Quick Start

Using the x402 SDK (Recommended)

import { wrapFetchWithPaymentFromConfig } from '@x402/fetch';
import { ExactEvmScheme } from '@x402/evm/exact/client';

const fetchWithPayment = wrapFetchWithPaymentFromConfig(fetch, {
  schemes: [{
    x402Version: 2,
    network: 'eip155:8453',
    client: new ExactEvmScheme(yourWalletSigner)
  }]
});

// Use it like normal fetch — payments are automatic
const response = await fetchWithPayment(
  'https://x402.silverbackdefi.app/api/v1/gas-price'
);
const data = await response.json();

Requirements

• A wallet with any accepted token on Base

• USDC: Works out of the box (uses ERC-3009, no approvals needed)

• All other tokens: One-time ERC-20 approval to Permit2 (0x000000000022D473030F116dDEE9F6B43aC78BA3)

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Free Endpoints

These endpoints are available without payment:

Endpoint	Description
/health	Server health check
/api/v1/pricing	View all endpoint prices
/api/v1/endpoints	List available endpoints

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Silverback Facilitator

Silverback operates its own x402 payment facilitator — the service that verifies, settles, and confirms payments on-chain. This means Silverback controls the full payment stack, with no reliance on third-party facilitators.

Facilitator URL: https://facilitator.silverbackdefi.app

What the Facilitator Does

When you send a signed payment with your API request:

1. Verify — The facilitator checks that your signature is valid, the token is whitelisted, and the amount covers the endpoint price

2. Settle — It submits the payment transaction on-chain (Base), transferring tokens from your wallet to the fee splitter

3. Confirm — Once the transaction is confirmed (~2 seconds), it returns a receipt with the transaction hash

You never interact with the facilitator directly — the x402 SDK and Silverback's API server handle this automatically.

Payment Protocols

The facilitator supports two settlement protocols:

Protocol	Used For	How It Works
ERC-3009	USDC	transferWithAuthorization — no approvals needed, sign-and-pay in one step
Permit2	All other tokens	permitWitnessTransferFrom — requires a one-time ERC-20 approval to Permit2

When you pay with USDC, the x402 SDK uses ERC-3009 for the simplest experience. For any other token (BACK, USDT, DAI, VIRTUAL, WETH, cbBTC), it uses Permit2.

Fee Splitter

All payments route through Silverback's on-chain Fee Splitter contract on Base:

Your Wallet → Fee Splitter Contract → splits into:
  ├── Net payment → Silverback Treasury (for buybacks & operations)
  └── Settlement fee → Protocol fee recipient

• $BACK payments: No fee is taken — 100% goes to treasury

• Stablecoin payments (USDC, USDT, DAI): 0.1% fee

• Blue-chip payments (WETH, cbBTC): 0.25% fee

• Ecosystem tokens (VIRTUAL): 0.1% fee

The fee split happens atomically on-chain — there's no manual step or delay.

Token Whitelisting

The facilitator only accepts curated, whitelisted tokens. This protects against scam tokens and ensures reliable settlement. The current whitelist includes 8 tokens across stablecoins, ecosystem tokens, and blue-chip assets.

New tokens can apply for listing on a case-by-case basis.

Facilitator Public Endpoints

The facilitator exposes several informational endpoints (no payment required):

Endpoint	Description
/health	Facilitator status, fee model, and configuration
/supported	Supported networks, tokens, and x402 version
/supported/tokens	All accepted tokens with live USD prices
/supported/convert?usd=0.02&token=BACK	Convert a USD amount to any token
/settle/stats	Total settlements, volume, and success rate
/discovery/resources	Browse all available paid resources

Settlement Details

Property	Value
Network	Base (Chain ID 8453)
Confirmation	~2 seconds (1 block)
x402 Version	2
Scheme	Exact
Facilitator Address	0x48380bCf1c09773C9E96901F89A7A6B75E2BBeCC
Fee Splitter	0x6FDf52EA446B54508f50C35612210c69Ef1C1d9a
Permit2	0x000000000022D473030F116dDEE9F6B43aC78BA3
Treasury	0xD34411a70EffbDd000c529bbF572082ffDcF1794

After a successful payment, the transaction hash is returned in the payment-response header so you can verify settlement on BaseScan.

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FAQ

Do I need an API key? No. x402 uses wallet-based authentication. Your payment signature is your access.

What if the request fails after I pay? The x402 protocol is atomic — payment only settles if the server returns a successful response.

Can I pay from any wallet? Yes, any wallet with supported tokens on Base. Hardware wallets, browser wallets, and programmatic wallets all work.

How do I approve tokens for Permit2? For non-USDC tokens, you need a one-time ERC-20 approval to the Permit2 contract. Most wallet interfaces can do this, or you can call approve() directly on the token contract with spender 0x000000000022D473030F116dDEE9F6B43aC78BA3.

Where do payments go? Payments route through Silverback's fee splitter contract. The settlement fee (if any) goes to protocol operations, and the net amount goes to the Silverback treasury — contributing to $BACK buybacks and staker rewards.