base-facts-mcp

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

1. 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.
2. 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.

Development

npm test drives the server over stdio like a real client, with empty wallets: no USDC is spent.