GuessMarket

MCP server for GuessMarket prediction markets. Gives AI agents full access to discover markets, analyze prices, check on-chain balances and positions, build trading transactions, and get smart contract ABIs.

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

Tools

Read-Only (API)

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

Read-Only (On-Chain)

Tool	Description
get_balance	Get a wallet's stablecoin (USDC/USDT) balance on any chain
get_allowance	Check how much stablecoin a market is approved to spend from a wallet
get_position	Get a wallet's YES shares, NO shares, and LP tokens on a specific market

These tools read directly from the blockchain via public RPC endpoints. No API keys required.

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. get_balance                 → Check your stablecoin balance
4. get_allowance               → Check if approval is needed
5. build_approve_tx            → Approve stablecoin spending (if needed)
6. build_buy_shares_tx         → Buy YES or NO shares
7. Sign and broadcast transactions with your wallet
8. get_position                → Verify your shares

Or combine steps 5-6 with build_buy_with_approval_tx which returns both transactions in order.

Sell Shares

1. get_position                → Check your share holdings
2. build_sell_shares_tx        → Sell shares back to the market
3. Sign and broadcast the transaction
4. get_balance                 → Verify stablecoin received

Provide Liquidity

1. build_approve_tx            → Approve stablecoin spending
2. build_add_liquidity_tx      → Deposit stablecoin, receive LP tokens
3. get_position                → Verify LP tokens received
4. 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/api/guessmarket/v1. Override with an environment variable:

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

Architecture

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

The MCP server provides market data (via REST API), reads on-chain state (via public RPC endpoints), 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