Manifold Betting API

A simple API for placing bets on Manifold Markets via URL pings. Allows you to bet using market slugs instead of market IDs.

Setup

Set the MANIFOLD_API_KEY environment variable with your Manifold API key
Get your API key from your Manifold profile page

Endpoints

GET /market/{slug}

Get market information by slug (JSON format).

Example:

GET /market/will-the-road-to-housing-act-become

Response:

{
  "id": "NcISOAqL6n",
  "slug": "will-the-road-to-housing-act-become", 
  "question": "Will the ROAD to Housing Act become law in 2025?",
  "probability": 0.20069534805930825,
  "isResolved": false,
  "resolution": null,
  "outcomeType": "BINARY",
  "url": "https://manifold.markets/bens/will-the-road-to-housing-act-become"
}

GET /info/{slug}

Get market information by slug (HTML format for AI crawlers and web browsers).

Example:

GET /info/will-the-road-to-housing-act-become

Response: Clean HTML page with:

Market question as heading
Current probability as percentage
Market status (open/resolved)
Trading instructions
Market details and links

Perfect for AI agents that prefer to crawl HTML instead of parsing JSON.

GET /bet/{slug}/{outcome}/{amount}

Place a bet on a market.

Parameters:

slug - Market slug (from the URL path)
outcome - YES or NO
amount - Amount in mana to bet (positive number)

Example:

GET /bet/will-the-road-to-housing-act-become/YES/10

Response:

{
  "success": true,
  "bet": {
    "id": "bet_id_here",
    "amount": 10,
    "outcome": "YES", 
    "shares": 12.34,
    "probBefore": 0.20,
    "probAfter": 0.21,
    "fees": {
      "platformFee": 0.1,
      "liquidityFee": 0,
      "creatorFee": 0.05
    }
  },
  "market": {
    "id": "NcISOAqL6n",
    "slug": "will-the-road-to-housing-act-become",
    "question": "Will the ROAD to Housing Act become law in 2025?",
    "url": "https://manifold.markets/bens/will-the-road-to-housing-act-become"
  }
}

Features

✅ Bet using market slugs instead of IDs
✅ Simple GET request interface
✅ Supports binary markets only
✅ Returns current probability for markets
✅ HTML endpoint for AI crawlers
✅ Web interface for testing
✅ Error handling and validation
✅ CORS enabled for web usage

Testing

The root URL provides a web interface for testing the API endpoints.

You can also test the HTML crawler endpoint directly:

https://your-api-url/info/will-the-road-to-housing-act-become

Error Handling

The API returns appropriate HTTP status codes and error messages:

400 - Invalid parameters (bad outcome, negative amount, etc.)
404 - Market not found
500 - Server error (missing API key, network issues, etc.)

AI Crawler Usage

The /info/{slug} endpoint is specifically designed for AI agents that prefer HTML over JSON:

Clean, semantic HTML structure
Probability displayed as percentage
Market status clearly indicated
Trading instructions included
Meta tags for description
No complex JavaScript or styling

Limitations

Only supports binary (YES/NO) markets
Requires MANIFOLD_API_KEY environment variable
No support for limit orders (uses market orders only)