polymarket-guard-mcp — Polymarket Prediction Markets MCP Server

Buy/sell positions on Polymarket prediction markets, paying in USDC with per-call billing via LemonCake. Read-only mode works with no credentials.

Installation

npx polymarket-guard-mcp

Or add to your MCP client (Claude Desktop, Cursor, etc.):

{
  "mcpServers": {
    "polymarket": {
      "command": "npx",
      "args": ["-y", "polymarket-mcp"],
      "env": {
        "POLYMARKET_PRIVATE_KEY": "0x<your-polygon-private-key>",
        "LEMONCAKE_SELLER_KEY": "<your-lemoncake-seller-key>"
      }
    }
  }
}

Environment Variables

| Variable | Required | Description | |---|---|---| | POLYMARKET_PRIVATE_KEY | For trading | Polygon wallet private key (0x-prefixed 32-byte hex). Required for positions, balance, and all trading tools. | | LEMONCAKE_SELLER_KEY | Optional | LemonCake seller key. Absent = Demo Mode (charges logged, no real billing). | | LEMON_CAKE_PERMIT | Optional | Client's ERC-2612 permit blob for non-custodial billing. Passed by the MCP client automatically when using LemonCake. |

Demo Mode

• Free/read tools work with zero env vars — no key needed.
• Account tools (get_positions, get_balance, get_trade_history) require POLYMARKET_PRIVATE_KEY.
• Trading tools require POLYMARKET_PRIVATE_KEY.
• LemonCake billing is a no-op in Demo Mode if LEMONCAKE_SELLER_KEY is absent — all tools still execute, charges are logged to stderr only.

Tools

Free (no charge)

| Tool | Description | |---|---| | list_markets | List active Polymarket markets with prices and volume | | search_markets | Search markets by keyword | | get_market | Get full market details by condition ID or slug | | get_order_book | Get live bid/ask order book for a market token |

$0.05 per call

| Tool | Description | |---|---| | get_positions | Your current open positions (shares held, P&L) | | get_balance | USDC balance and contract allowances | | get_trade_history | Past trades with prices and timestamps |

$0.10 per call

| Tool | Description | |---|---| | place_market_order | Buy/sell at market price (FOK with slippage tolerance) | | place_limit_order | Place a GTC/FOK/IOC limit order at a specific price | | cancel_order | Cancel an open limit order by ID | | redeem_positions | Claim USDC winnings from resolved markets |

Example Usage

# Find markets about the 2024 US election
search_markets(query="US election 2024")

# Get the order book for a specific outcome token
get_order_book(token_id="0x...")

# Check your current positions
get_positions()

# Buy 100 YES shares on a market (limit order at 0.65 = 65 cents/share)
place_limit_order(
  token_id="0x...",
  side="BUY",
  price=0.65,
  size=100
)

# Buy using market order with 2% slippage tolerance
place_market_order(
  token_id="0x...",
  side="BUY",
  amount=50  # $50 USDC
)

# Claim winnings after market resolves
redeem_positions(condition_id="0x...")

Architecture

• Market data: Polymarket Gamma API (gamma-api.polymarket.com)
• Trading: Polymarket CLOB API (clob.polymarket.com) with L1 EIP-712 auth
• Chain: Polygon (chainId 137)
• Token: USDC on Polygon (6 decimals)
• Billing: LemonCake USDC pay-per-call (@lemon-cake/mcp-sdk)

Authentication Note

Polymarket's CLOB API uses L1 auth: EIP-712 typed-data signatures over each request. This implementation includes the complete request structure. For full production signing (real orders), install ethers and integrate the Wallet.signTypedData() method — the current build uses a placeholder signature that will receive a 401 from the CLOB for authenticated endpoints.

Full signing integration:

npm install ethers

import { ethers } from "ethers";
const wallet = new ethers.Wallet(process.env.POLYMARKET_PRIVATE_KEY!);
const sig = await wallet.signTypedData(domain, types, value);

Pricing & Billing

| Action | Cost | |---|---| | Browsing markets | Free | | Checking positions / balance | $0.05 USDC | | Placing / cancelling orders | $0.10 USDC | | Claiming winnings | $0.10 USDC |

Billing is handled by LemonCake — USDC pay-per-call infrastructure for MCP tools. No subscription, no monthly fees. You pay only when you call a tool.

Related MCP Servers

• alpaca-guard-mcp — Traditional stocks via Alpaca brokerage with daily USD cap
• tokenized-stock-mcp — Tokenized US stocks (Dinari dShares) via USDC
• xstocks-mcp — On-chain tokenized stocks via Solana Jupiter DEX
• pay-per-call-mcp — USDC micropayments for any HTTP API

License

MIT