GuessMarket MCP Server

MCP server for GuessMarket prediction markets. Gives AI agents full access to discover markets, analyze price history, view wallet portfolios, build trading transactions, and get smart contract ABIs.

Live on 5 EVM chains: Ethereum, Base, Polygon, BSC, and PulseChain.

Tools

Read-Only

| Tool | Description | |------|-------------| | list_markets | List prediction markets with filters for status and chain | | get_market | Get detailed market info: question, YES/NO odds, volume, liquidity, end time | | get_market_history | Get timestamped price history for trend analysis | | get_networks | Get all supported chains with contract addresses | | get_portfolio | Get a wallet's trading activity across all markets | | get_abi | Get smart contract ABI for custom integrations |

Transaction Builders

All transaction builders return unsigned EVM transaction objects. Sign with your wallet and broadcast to the chain. Amounts are human-readable (e.g. "10.5") and automatically converted to the correct decimals per chain (6 for USDC, 18 for BSC USDT).

| Tool | Description | Key Parameters | |------|-------------|----------------| | build_approve_tx | Approve stablecoin spending for a market | market_address, amount (or "max" for unlimited), chain_id | | build_buy_shares_tx | Buy YES or NO outcome shares | market_address, outcome, amount, chain_id, min_shares (slippage) | | build_sell_shares_tx | Sell YES or NO outcome shares | market_address, outcome, shares, chain_id, min_usdc (slippage) | | build_add_liquidity_tx | Add stablecoin liquidity, receive LP tokens | market_address, amount, chain_id | | build_remove_liquidity_tx | Burn LP tokens, receive stablecoin back | market_address, lp_tokens, chain_id | | build_claim_winnings_tx | Claim winnings from a resolved market | market_address, chain_id | | build_create_market_tx | Create a new prediction market | question, end_time (unix timestamp), chain_id | | build_buy_with_approval_tx | Approve + buy in one call (returns 2 ordered transactions) | market_address, outcome, amount, chain_id, min_shares (slippage) |

Slippage Protection

build_buy_shares_tx and build_sell_shares_tx accept optional slippage parameters (min_shares and min_usdc). When set to 0 (default), the server returns a warning. Set a minimum to protect against front-running.

Trading Flow

Buy Shares

1. list_markets               → Find a market to trade
2. get_market                  → Check current odds and liquidity
3. build_approve_tx            → Approve stablecoin spending
4. build_buy_shares_tx         → Buy YES or NO shares
5. Sign and broadcast both transactions with your wallet

Or combine steps 3-4 with build_buy_with_approval_tx which returns both transactions in order.

Sell Shares

1. build_sell_shares_tx        → Sell shares back to the market
2. Sign and broadcast the transaction

Provide Liquidity

1. build_approve_tx            → Approve stablecoin spending
2. build_add_liquidity_tx      → Deposit stablecoin, receive LP tokens
3. build_remove_liquidity_tx   → Later: burn LP tokens to withdraw

Create a Market

1. build_create_market_tx      → Deploy a new prediction market
2. Sign and broadcast — the new market address is in the tx receipt

Transaction Response Format

{
  "transaction": {
    "to": "0x...",
    "data": "0x...",
    "chainId": 8453,
    "value": "0x0"
  },
  "description": "Buy YES shares for 10 USDC on market 0x... (Base Mainnet)",
  "meta": {
    "chain": "Base Mainnet",
    "stablecoin": "USDC",
    "outcome": "YES",
    "function": "buyShares(uint8,uint256,uint256)"
  },
  "warnings": []
}

Quickstart

Claude Desktop

Add to your claude_desktop_config.json:

{
  "mcpServers": {
    "guessmarket": {
      "command": "npx",
      "args": ["-y", "guessmarket-mcp"]
    }
  }
}

Claude Code

Add to your project with the CLI:

claude mcp add guessmarket -- npx -y guessmarket-mcp

Or add to .mcp.json in your project root:

{
  "mcpServers": {
    "guessmarket": {
      "command": "npx",
      "args": ["-y", "guessmarket-mcp"]
    }
  }
}

VS Code

Add to your VS Code settings or .vscode/mcp.json:

{
  "mcp": {
    "servers": {
      "guessmarket": {
        "command": "npx",
        "args": ["-y", "guessmarket-mcp"]
      }
    }
  }
}

Supported Chains

| Chain | Chain ID | Stablecoin | |-------|----------|------------| | Ethereum | 1 | USDC (6 decimals) | | Base | 8453 | USDC (6 decimals) | | Polygon | 137 | USDC (6 decimals) | | BSC | 56 | USDT (18 decimals) | | PulseChain | 369 | USDC (6 decimals) |

Configuration

No API keys required — the server uses the public GuessMarket REST API.

Custom API URL

By default the server connects to https://guessmarket.com/wp-json/guessmarket/v1. Override with an environment variable:

{
  "mcpServers": {
    "guessmarket": {
      "command": "npx",
      "args": ["-y", "guessmarket-mcp"],
      "env": {
        "GUESSMARKET_API_URL": "https://your-instance.com/wp-json/guessmarket/v1"
      }
    }
  }
}

Architecture

AI Agent  <-->  MCP Server  <-->  GuessMarket REST API
   |                                      |
   |                                5 EVM Chains
   |                            (Ethereum, Base, Polygon,
   |                               BSC, PulseChain)
   |
   └── Signs & broadcasts unsigned transactions on-chain

The MCP server provides market data (via REST API) and builds unsigned transactions (via local ABI encoding). The agent signs transactions with its own wallet and broadcasts directly to the blockchain.

Requirements

• Node.js 18 or later (uses native fetch)

Development

npm install
npm run build
node build/index.js

License

MIT