The rail AI agents use to trade prediction markets.

What a session looks like

A real exchange, captured on 2026-09-02. Tool results are abridged; the numbers are the venue's.

you   find markets about bitcoin and quote 100 shares on the favourite

agent find_markets("bitcoin")
      {"markets": [{"venue": "polymarket",
        "title": "Will the price of Bitcoin be above $72,000 on September 2?",
        "yes_price": 0.991, "best_bid": 0.988, "best_ask": 0.994,
        "spread": 0.006, "volume_24h": 196435, "market_id": "4430…2778"}, …]}

agent quote_cost("polymarket", "4430…2778", "BUY", 100)
      {"cost": {"fillable": true, "filled_size": 100, "avg_price": 0.994,
        "notional": 99.4, "slippage_vs_best": 0.0,
        "levels_consumed": [{"price": 0.994, "size": 100}]},
       "fees": {"fees_enabled": true, "fee_type": "crypto_fees_v2", "taker_only": true}}

agent 100 YES on "Bitcoin above $72,000 on Sept 2" costs $99.40 at 0.994,
      all at one level, no slippage. It pays $100 if it resolves YES: 0.6%
      gross before the taker fee. place_order is in dry-run; say the word
      and I will read back the intent before anything is signed.

How it compares

Against the raw venue APIs and the three products that actually compete today. Every cell is verified from their own docs and dated in the README.

Built from the things the raw API gets wrong

Each of these was found by driving the venues live, then encoded so an agent never has to rediscover it.

1. The book arrives worst-first

   Polymarket's raw orderbook lists bids ascending and asks descending, so bids[0] is the worst level. Every model's prior says index 0 is best. oddsrail normalises both venues to best-first and walks the book to quote what a size actually costs.

2. Rejections don't raise

   The exchange models a rejected order as a return value, not an exception. Reported carelessly, a rejection reads to an agent as a resting order. oddsrail branches on it: accepted: false, nothing attributed, and an unrecognised response shape is never reported as posted.

3. Geoblocks look healthy until the order

   Restricted jurisdictions are enforced at order placement. Public reads answer normally, so everything works right up to the trade. oddsrail classifies every failure shape (jurisdiction, network filter, ISP interstitial, a missing local CA bundle) and gives the agent an actionable hint instead of a retry loop.

4. "Account trades" returns everyone's

   The SDK call that sounds like your fills returns the market's public tape. oddsrail reads the operator's activity feed by wallet, with transaction hashes.

5. Kalshi has no yes/no side

   Everything is quoted from the YES book as bid and ask; prices are dollar strings, not cents. Getting the translation backwards silently takes the opposite position. oddsrail lets the agent say outcome=no, action=buy and translates it, tested exhaustively rather than by example.

6. A price gap is not an edge

   Identical wording on two venues does not mean identical settlement. oddsrail pairs candidates by similarity and close date, then audits resolution sources, UMA status and structure before anyone calls it arbitrage.

What's inside

30 read-only tools that need no keys, 9 trading tools that respect dry-run and the operator's guardrails, and four prompts that encode the order of operations that keeps an agent out of trouble.

Where the builder code goes

Nothing is proxied and nothing is stored. The only thing oddsrail adds to your order is a public attribution tag, signed by your key, on your machine.

1. 1. your agentAny MCP client
   • Claude Code, Desktop, Cursor and others
   • speaks plain intent: "buy 100 YES at 0.62"
2. 2. oddsrail, on your machineChecks, then signs
   • guardrails, then the dry-run gate: simulate unless ODDSRAIL_DRY_RUN=0
   • book-walked cost, jurisdiction preflight
   • builder code placed in the order struct, then signed with your key
3. 3. venuePolymarket CLOB, Kalshi
   • your own credentials
   • rejections branched, never reported as resting
   • 0 bps builder fee added
4. 4. on-chainCTF Exchange V2
   • every OrderFilled event carries the code
   • attribution is public and auditable
   • weekly pool share paid by Polymarket

How it pays for itself without charging you

# the whole configuration
export ODDSRAIL_DRY_RUN=1          # default: simulate, papered
export ODDSRAIL_BUILDER_CODE=0x…   # optional: yours
export ODDSRAIL_MAX_ORDER_NOTIONAL=25
export POLYMARKET_PRIVATE_KEY=…    # only to trade
export POLYMARKET_RELAYER_API_KEY=… # only for gasless ops
export KALSHI_KEY_ID=…             # only for Kalshi private

# then, in any MCP client
"find markets about the world cup and
 quote the cost of 100 shares on the favourite"

Live from the builder program

Fetched in your browser from Polymarket's public data API. Nothing here is a screenshot. Reward epochs run Sunday 00:00 to Saturday 23:59 UTC.