An MCP server for AI agents that trade or move money on Base. Each tool calls Base Token Facts and pays for the call itself in USDC over x402, from a small wallet you control. Every answer is read at one block and says which.

Tool	Price	Answers
`base_token_verdict`	$0.01	Before buying a token: risk level, score and flags (proxy, mint, pause, blacklist, owner, DEX liquidity), each with its on-chain fact
`base_token_sellcheck`	$0.005	Honeypot and tax check: simulates a small buy and immediate sell on the deepest pool, returns buy/sell tax, round-trip loss
`base_token_batch_screen`	$0.03	The same simulation for up to 10 tokens in one call and one payment (per token: taxes, round-trip loss, flags)
`base_token_sellcheck_size`	$0.01	The same check at your trade size (`amountEth`, 0.001 to 10 ETH): tax, round-trip loss, buy price impact and a depth warning when the size is larger than the pool can absorb
`base_token_facts`	$0.005	ERC20 metadata, owner, proxy and implementation, admin selectors in the bytecode
`base_wallet_snapshot`	$0.002	ETH and USDC balances, nonce, contract or not
`base_gas`	$0.001	Base fee, priority fee, gas price
`base_tx_summary`	$0.003	Status, fee and decoded ERC20 transfers of a transaction
`basename_resolve`	$0.002	`name.base.eth` to address, or address to its verified primary Basename
`base_facts_budget`	free	What this session has spent

Facts and heuristics, not financial advice. API docs and live revenue counter: https://base-facts.yankii.fr and https://base-facts.yankii.fr/stats

Setup

Make a dedicated wallet and put a little USDC on it, on the Base network (1 USDC pays for 100 verdicts). No ETH is needed: the x402 facilitator pays the gas. Never use your main wallet.
Add the server to your MCP client, for example claude_desktop_config.json:

{
  "mcpServers": {
    "base-facts": {
      "command": "npx",
      "args": ["-y", "base-facts-mcp"],
      "env": {
        "X402_PAYER_FILE": "/path/to/payer.json",
        "MAX_PRICE_USD": "0.03",
        "SESSION_BUDGET_USD": "1"
      }
    }
  }
}

payer.json is { "privateKey": "0x..." }; X402_PRIVATE_KEY works too. Without either, the server uses ~/.base-facts-mcp/payer.json when it exists.

Every setting also exists as an option, for hosts that pass only command and args (Preste): --payer-file <path>, --max-price <usd>, --budget <usd>, --api <url>. See integrations/preste/ for the Preste config and skill.

Spending safety

Each tool also has its own ceiling (its published price: gas 0.001, batch 0.03, and so on): a route that asks for more than its published price is refused, whatever MAX_PRICE_USD says.
If the answer to a paid call is lost after the payment was signed, the amount is counted against the session budget (the payment may have settled) and the tool says so: check the wallet before retrying.
MAX_PRICE_USD (default 0.03): the client refuses to sign any single payment above it.
SESSION_BUDGET_USD (default 1): once reached, the client stops signing until restarted.
BASE_FACTS_PAY_TO (default: the official address when using the default API): the only recipient the client will sign for. Required with a custom BASE_FACTS_URL; without it nothing is signed. The client also signs only Base USDC (0x8335…2913).
Only USDC on Base (eip155:8453) is ever signed.
A refused or failed call (4xx/5xx) cancels the settlement: you are not charged, and the tool says charged: false with the reason (for example not enough USDC).
Paid calls run one at a time so the budget count stays exact.