oddsrail

The rail AI agents use to trade prediction markets.

An MCP server that gives any agent (Claude Code, Claude Desktop, or anything MCP-compatible) prediction-market access across Polymarket and Kalshi: market search, orderbooks, price history, positions, and order routing — with on-chain builder-code attribution on Polymarket — plus two premium signal tools (in-play overshoot/fade detection, resolution dispute-risk).

Free to use, and free of fees. oddsrail ships with a project builder code registered at 0 bps, so orders routed through it are attributed without adding a single basis point to anyone's trade. The project's income is a share of Polymarket's weekly builder reward pool — paid by Polymarket's own program, not by you. Running your own builder profile instead is one environment variable (ODDSRAIL_BUILDER_CODE), and server_info always tells you which code is in use. No fee tiers, no paywalled tools, no account required.

How oddsrail compares

Verified against each alternative directly (their repos, live endpoints, and registry entries — August 2026), not from their marketing:

¹ The raw Polymarket API has the endpoints — and models rejections as ok:false return values, orders its books worst-first, ships a trades endpoint that returns the market's public tape, and enforces an undocumented $1 minimum notional. oddsrail exists because we hit every one of those and encoded the fix.

² Kalshi prices are dollar strings (integer cents were removed 2026-03), its orderbook is bids-only on both sides, and its current SDK requires Python ≥3.13. All normalised here.

Where the others are honestly ahead: Parsec covers 5 venues to our 2 and has websocket streaming; Crosswire's settlement-audit output on its one covered pair is deeper than our resolution_criteria, and it takes x402 micropayments natively; hosted services need zero install. Our bet is that a trading agent cares more about correctness, auditability, and keeping 100% of its economics than about any of those.

Quickstart

Python 3.11+ required.

pip install oddsrail

claude mcp add --transport stdio oddsrail -- oddsrail

Or from a clone, without installing:

python3 -m venv .venv && .venv/bin/pip install -r requirements.txt

claude mcp add --transport stdio oddsrail -- /abs/path/to/oddsrail/.venv/bin/python -m oddsrail.server

Then ask the agent: "search markets about the World Cup final and run the overshoot signal on the favorite".

How attribution works (CLOB V2, verified Aug 2026)

1. Get your builder code (a bytes32) at polymarket.com → Settings → Builders. Set your fee rates there: taker up to 100 bps, maker up to 50 bps — additive on top of platform fees, settled to your builder wallet.
2. export ODDSRAIL_BUILDER_CODE=0x... where the server runs.
3. Every order any agent routes through place_order has the code placed in the V2 order struct's builder field before signing — attribution is on-chain, visible in every OrderFilled event on CTF Exchange V2.
4. Verify with the builder_stats tool (public builder-trades endpoint + leaderboard).

If you skip this, orders carry the bundled oddsrail builder code (0xa576c5ce…, registered at 0 bps maker / 0 bps taker) — costing you nothing and funding the project. If you set your own, yours wins; the default is a default, not a lock-in.

Environment variables

Status

Offline tests: 81 tests covering the paths where a bug costs money — the Kalshi yes/no→bid/ask translation, Kelly sizing, book walking, cross-venue pairing, signal edge cases, the dry-run safety net, and jurisdiction-failure handling (a geoblock must never read as an empty search result or a resting order). They need no keys and no network:

pip install -e ".[dev]" && pytest

CI runs them on Python 3.11, 3.12 and 3.13 on every push and pull request.

Live venues: every read tool and both dry-run order paths have been driven end-to-end against real Polymarket and Kalshi through a real MCP client session. Two attributed Polymarket orders (a buy and a sell) have been placed and confirmed on-chain.

Not yet exercised live: the Kalshi order placement path. Its request shape is unit-tested and its endpoint verified, but no order has been sent to a real Kalshi account, because the author does not yet have a funded, verified one. This is untested, not untestable. Treat kalshi_place_order as unproven and start in dry-run.

Where this works

Two different things can stop oddsrail from trading, and they have opposite remedies. One is a venue restriction, enforced at the order. The other is a network filter, which breaks the connection itself.

Polymarket restrictions. Polymarket publishes its restricted-jurisdiction list as an API reference: https://docs.polymarket.com/api-reference/geoblock. There are three tiers. OFAC-sanctioned jurisdictions — Iran, Syria, Cuba, North Korea, and the Crimea, Donetsk and Luhansk regions of Ukraine — are blocked on both the frontend and the API, with no new orders and no closing of existing positions. A longer second tier is close-only on both the frontend and the API: existing positions can be closed, new ones cannot be opened. It includes the United States, the United Kingdom, France, Germany, Italy, Poland, Slovakia, Belgium, Singapore, Australia, New Zealand, Brazil, Russia, Taiwan, Thailand and the Canadian provinces of Ontario, Quebec, British Columbia and Alberta. A third group — Ireland, Japan, Malta (sports only) and the Netherlands — is close-only on Polymarket's frontend, with the API explicitly not restricted.

Note the shape of that failure: it lands on the order, not the connection. Public reads answer normally, so oddsrail will look like it is working right up until an order is rejected. Verified against Polymarket's documentation on 2026-08-31; Polymarket updates the list without notice, so read the URL rather than this paragraph.

Kalshi restrictions. Kalshi is a single CFTC-designated contract market and it does admit members outside the United States — but its Member Agreement §VI names a long list of Restricted Jurisdictions whose members may not trade Event Contracts, among them Australia, Belgium, Canada, France, Ireland, Italy, New Zealand, Poland, Portugal, Singapore, Switzerland, the United Kingdom, Hungary, India, the United Arab Emirates and mainland China. The list is published in Kalshi's Exchange Notice of 22 June 2026 (https://kalshi-public-docs.s3.amazonaws.com/regulatory/notices/Kalshi%20Exchange%20Notice%20(Updated%20Member%20Agreement)%20(22%20June%202026).pdf), and Kalshi reserves the right to change it. The same section is explicit that the restriction applies only to trading Event Contracts and does not by itself bar membership or non-trading access, so oddsrail's Kalshi read tools stay usable even where its order tools do not.

The two lists overlap heavily. Kalshi is not a general fallback for a Polymarket-restricted operator, and the difference runs in both directions. Among the jurisdictions polymarket.com lists as close-only, Germany, Brazil, Slovakia and the United States are not on Kalshi's restricted list; Japan and the Netherlands are restricted by neither API (only by Polymarket's frontend). Check both lists for your own jurisdiction rather than assuming the other venue is open — and the US case has its own wrinkle.

The United States. polymarket.com — the venue oddsrail talks to — is close-only for the US. Polymarket separately operates Polymarket US (polymarket.us), run by QCX LLC as a CFTC-regulated Designated Contract Market. oddsrail does not support it. It is a different API host, a different authentication model (API-key headers rather than EIP-712 wallet signatures), a different SDK and a different funding rail. A polymarket.us account and its keys will not work with this server. Kalshi does not list the US as restricted, so for a US operator Kalshi is the venue oddsrail can actually reach — with no builder-code attribution, since Kalshi's REST API has no such field.

Network filters. Separately from any venue rule, a national filter can block the domains outright. Turkey does this: Polymarket does not restrict Turkey, and Turkey is not on Kalshi's list either, but Turkish ISPs block polymarket.com. That is a connectivity problem, not an eligibility one, and it looks different — DNS failures, TLS errors, resets, or an ISP interstitial page served where JSON was expected. oddsrail classifies both shapes and tells the calling agent which one it hit.

Eligibility is the operator's, not the tool's. oddsrail is self-hosted and non-custodial, which is a real advantage and also means you hold the account and you make the venue's representations — there is no intermediary making them for you. Polymarket's trading flow requires an attestation that you are not a U.S. person, are not located in a restricted jurisdiction, and are not "using a VPN or other measures to circumvent or attempt to circumvent" restrictions, and states that Polymarket reserves the right to put a non-compliant wallet in close-only mode. Kalshi's §VI is a representation about where you are domiciled, organized and located, re-made each time you place an order. server_info reports Polymarket's geoblock verdict for this machine's IP, but a technical probe is not a compliance check: the terms bind on residence, citizenship and incorporation, not on egress IP. Read the terms; if any of this matters to you, get your own legal advice. Nothing here is legal advice.

The signal logic, the MCP layer and the whole test suite run fine offline regardless.

Kalshi (venue #2)

Kalshi is bring-your-own-key and single-tenant by design: the operator supplies their own API key, trades their own account, and this server caches nothing. That is deliberate — Kalshi's Developer Agreement limits API use to a member's own trading (§3), bars facilitating other members' trading (§3.2) and sublicensing the API (§3.7), and restricts storing/sharing API data (§3.1). A hosted multi-tenant Kalshi service would not be compliant; a self-hosted one is.

Attribution does not exist here. Kalshi Builder Codes are a Solana/DFlow/Jupiter integration — there is no builder or affiliate field anywhere on the REST API, so Kalshi order flow cannot be attributed or monetised the way Polymarket's can. Kalshi is in oddsrail for coverage and signal reach, not for routing revenue.

Two shapes on this API are easy to get wrong, so oddsrail normalises both:

• Prices are dollar strings, not cents ("0.5600"), sizes are fixed-point strings ("10.00"); the legacy integer-cent fields were removed in March 2026. All arithmetic uses Decimal.
• The orderbook is bids-only on both sides. yes_dollars and no_dollars are both bid ladders, ascending — so the best bid is the last element, and a NO bid at $0.99 is a YES ask at $0.01. kalshi_get_orderbook returns a conventional best-first bid/ask view of the YES book plus the raw ladders.

Order placement speaks natural terms — outcome (yes/no), action (buy/sell), price = probability of that outcome — and translates to Kalshi's YES-book bid/ask internally (buy NO @ 0.25 becomes ask @ 0.75). That translation is exhaustively unit-tested (tests/test_money_paths.py), since it is the obvious place to ship an inverted-position bug.

Credentials: KALSHI_KEY_ID plus KALSHI_PRIVATE_KEY_PATH (PKCS#8 PEM) or KALSHI_PRIVATE_KEY. Set KALSHI_DEMO=1 to hit the demo environment. Read tools need no key at all.

Cross-venue tools

• find_markets(query) — searches Polymarket and Kalshi in one call and returns one normalised shape per market: venue, market_id (the id that venue's order tool takes), title, yes/no price as probabilities in (0,1), best bid/ask, spread, 24h volume, close time, and trade_with naming the tool to call. Use this when you do not already know the venue.
• quote_cost(venue, market_id, side, size) — what a size would actually cost, by walking the book rather than reading the top level. Returns average fill price, slippage vs best, notional, levels consumed, and whether the size is fillable at all — plus Polymarket's per-market fee schedule where it publishes one. Kalshi does not publish fees in its market payload, so they are reported as unknown rather than estimated.
• compare_venues(query) — candidate same-event listings across venues. Not an arbitrage scanner. Matching an event across venues is an unsolved entity-resolution problem: naive title overlap cheerfully pairs a Brazilian election with a Ukrainian one and reports a 70-point "gap" that is fiction. Two gates apply (title similarity ≥ 0.5 and close dates within a week), so it usually returns nothing — which is the honest answer. A price delta between candidates is reported as yes_price_difference, never as profit.

Kalshi search

Kalshi has no text-search endpoint. oddsrail searches by event (the human-readable index, with with_nested_markets) rather than paging tens of thousands of machine-named markets, and matches on word boundaries — without that, "fed" matches "German Bundestag" and a Fed-rate query returns German election markets. Results carry truncated, because a bounded scan means an empty result is not proof a market does not exist.

Order lifecycle & discovery

• order_status(order_id) — resting / partially_filled / filled / gone, with size_matched. The answer an agent needs after place_order.
• my_fills(), my_positions() — the operator's executions and holdings, no address juggling. (Fills come from the Data API activity feed — the SDK's list_account_trades returns the market's public tape and is not used.)
• cancel_all_orders() — kill switch: flatten every resting order at once.
• resolution_criteria(venue, market_id) — the full resolution contract: what resolves YES, who resolves it, from which sources. Read it before trusting a price.
• closing_soon(hours) — markets closing within N hours on either venue, where activity concentrates.

Workflow prompts

MCP prompts show up in clients as ready-made workflows, and they encode the order of operations that keeps an agent out of trouble — the sequencing is the expertise, which a flat tool list cannot convey.

• /find_fade_setup(query, bankroll) — signal → book → cost → resolution → size → dry-run, with the rejection criteria at each step
• /check_cross_venue_edge(query) — candidates → settlement audit → cost on both legs, and says plainly when the answer is "no edge"
• /daily_review — positions, resting orders, fills, closing-soon, attribution

Risk & settlement

• settlement_audit(polymarket_id, kalshi_ticker) — the check that decides whether a cross-venue price difference is an edge or a mismatch. Compares close times, resolution sources, UMA dispute status and market structure on live data with no pre-curated pair list, returning ok / caution / block with reasons — and listing the checks it did not perform.
• position_size(bankroll_usd, price, fair_value) — fractional-Kelly sizing, capped, refusing negative-edge bets, returning its own assumptions.

Tools (32)

• search_markets, get_market, get_orderbook, price_history, get_positions — read-only, no keys
• overshoot_signal — premium: fresh panic-jump detection + this market's historical reversion tendency (ported from the polymarket-wc analyzer)
• dispute_risk — premium: transparent 0–100 heuristic for contested (UMA-dispute-prone) resolutions
• place_order, cancel_order, open_orders — trading, dry-run by default. price is a probability in (0,1), size is in SHARES, and the exchange enforces a $1 minimum notional on marketable orders. Trading tools carry destructiveHint annotations so clients can gate them.
• builder_stats — attribution verification + public builder leaderboard
• find_markets, compare_venues, quote_cost — cross-venue (above)
• server_info — config status, per-venue

Kalshi: kalshi_search_markets, kalshi_get_market, kalshi_get_orderbook, kalshi_get_trades, kalshi_balance, kalshi_positions, kalshi_open_orders, kalshi_place_order, kalshi_cancel_order.

Stack notes

• Official unified SDK polymarket-client (0.6.x): AsyncPublicClient for data, AsyncSecureClient.place_limit_order(..., builder_code=...) for attributed orders. The legacy py-clob-client is archived and cannot attach builder codes — do not use it.
• MCP SDK 2.0: MCPServer from mcp.server.mcpserver (the old mcp.server.fastmcp.FastMCP import is gone in 2.x).
• Kalshi is on plain httpx + cryptography, not the official SDK: kalshi-python-sync requires Python >=3.13 and re-releases weekly in lockstep with the spec version. Auth is RSA-PSS(SHA256, salt=digest length) over str(unix_ms) + METHOD + path, where the path includes /trade-api/v2 and excludes the query string. Base URL is now external-api.kalshi.com.
• x402 (planned): the official x402 PyPI package (v2.20+) can wrap MCP tools directly (x402.mcp, payment rides in tool-call _meta), but its MCP helpers currently target mcp 1.x — integrating means pinning mcp>=1.28,<2 or waiting for the 2.x-compatible release. Mainnet settlement needs a facilitator (Coinbase CDP: 1,000 free settlements/mo, then $0.001). Keep free tiers of both signals so registries can index the server.

Who this is for

Polymarket's public builder leaderboard shows what a single operator routing their own flow is worth. Pulled 2026-08-31 via this server's own builder_stats tool — re-run it, the numbers move:

The instructive rows are the small ones: MagicMarkets routes $901K/week with a single active user; Jupiter $515K with one; Sharkbetting $1.15M with two. Those are bot operators routing their own flow — which is exactly who this is built for.

Roadmap

1. Live smoke test from an unblocked network — done 2026-08-23, all tools pass
2. Register builder code (polymarket.com → Settings → Builders), set fees to 0 bps at launch, export ODDSRAIL_BUILDER_CODE; first attributed order on a tiny size
3. Kalshi as venue #2 — done 2026-08-23, 9 tools, verified live
4. x402 paid wrapping for the two signals once the mcp-2.x conflict clears
5. Registry listings: official MCP registry (mcp-publisher, PyPI mcp-name: marker), Smithery (needs public streamable-HTTP + a free tool for their scanner), Glama (glama.json)

Listing / distribution

• GitHub: https://github.com/hmesutozsoy/oddsrail (public, MIT)
• Glama: auto-crawls GitHub; glama.json in the repo root claims maintainership.
• PyPI: https://pypi.org/project/oddsrail/ — pip install oddsrail
• Official MCP registry: listed as app.oddsrail/polymarket-kalshi-arbitrage (published 2026-08-30, status active). Re-publish after a version bump with mcp-publisher publish; keep server.json's version in step with pyproject.toml or the registry rejects it.
• Smithery: requires a public HTTPS streamable-HTTP endpoint — available once oddsrail is hosted rather than run locally over stdio.