// API + MCP · LIVE ON KALSHI + POLYMARKET
Your orders,
filled for less.
That's the mission — and your receipts, not our claims, will prove it. Live today: one API and a hosted MCP server for Kalshi and Polymarket, with hard server-side risk limits on every order and keys that stay yours.
We onboard every beta trader personally. Talk to us first.
20 minutes with the founder · a small group onboarded each week · free during beta
# one routed, risk-checked order — one REST call
curl -X POST https://api.trymithril.com/v1/orders \
-H "Authorization: Bearer mk_live_7f3c…" \
-d '{
"subaccount_id": "sub_alpha",
"market_id": "mkt_2f9a1c",
"action": "buy",
"order_type": "limit",
"quantity": "250",
"price": "0.42"
}'// LIVE TODAY · BUILT FOR BOTS AND AGENTS
Your trader is a program. We built for that.
The REST API and the hosted MCP server are live now: idempotent orders, websocket fills, deterministic errors — and Claude, GPT, or your own agent trading inside hard server-side limits. Point an agent at it right now.
Idempotent placement
Idempotency keys on order placement — a flaky retry never double-fires. Deterministic error codes you can branch on.
Websocket fills
Fill and position streams over websocket, plus a status page you can actually check and honest rate limits.
MCP-native
A hosted MCP server exposes search_markets, place_order, get_portfolio and more — so Claude, GPT, or your own agent trades inside your limits.
# an AI agent, trading inside your limits
› search_markets("fed cuts june")
› place_order(mkt_2f9a1c, buy, 250 @ 0.42)
› get_portfolio()
MCP · https://mcp.trymithril.com/mcp · tools: search_markets, place_order, cancel_order, get_portfolio
// 01 / ROUTE
Best net price, not best displayed price.
The same market often trades at different prices on Kalshi and Polymarket — and their fee models differ more than their prices. Mithril compares net cost after fees and splits your fill across venues automatically. Where a market lives on one venue only, the same order API executes there directly.
kalshi 34.5¢ · taker fee formula
polymarket 34.2¢ · flat bps
→ Mithril fills at the best net cost after fees
// 02 / WORK
Push size without making a splash.
Thin books punish size. Send us the parent order; we slice it, pace it, and respect your slippage cap — so a 20,000-contract order doesn't announce itself to the whole book. Or rest inside the spread and earn maker pricing instead of paying to cross it.
Sliced marketable-limit: child orders with randomized sizing and timing under a max-slippage bound, so size never sweeps four levels of a thin book.
Passive post: rest at or inside the spread, earn maker pricing, auto-reprice on a peg, cancel on adverse moves. On a wide long-tail market, the spread is the whole cost of the trade.
// 03 / PROVE
We measure it, so you don't take it on faith.
Every fill comes back with a receipt: what you paid, what a naive market order would have cost, and fees per venue. We won't put a savings number on this page until your receipts produce it — beta exists to prove, on your own flow, that your net cost with Mithril beats going to the venue directly. That's the deal.
// 04 / PROTECT
Hard limits before any order leaves.
Notional caps, per-market limits, slippage bounds, and a kill switch — enforced server-side before any order reaches a venue. Run bots, or let an AI agent trade, without handing over the ability to blow up the account. Your keys stay envelope-encrypted (X25519), decrypted only to sign; we never take custody of funds.
Subaccounts isolate strategies or clients, each with its own credentials, positions, and limits — one account, many books. Every order passes your limits before it touches a venue, whether it came from your code or from an agent.
// PRICING
If we don't save you money, don't pay us.
No card required · full API access · founder-onboarded, a small group each week
- ✓Kalshi + Polymarket · both live
- ✓Fee-aware smart order routing
- ✓Worked orders for thin books
- ✓Execution receipt on every fill
- ✓Server-side risk limits & kill switch
- ✓Hosted MCP server for AI agents
Mithril is free during beta. After beta: a few basis points on filled volume — and only above a monthly notional threshold, so small size stays free.
The receipts keep us honest: every fill shows what you paid, what the naive alternative cost, and what you saved. If the receipts don't show we save you more than we cost, don't pay us. Manage everything — credentials, subaccounts, API keys, and risk limits — from one place.
// FAQ
The details, answered straight.
How does Mithril get me a better price?+
Two ways. Routing: we compare the net cost after fees on Kalshi and Polymarket — their fee models differ more than their prices — and split the fill across venues when that's cheaper. Working: large orders are sliced and paced into thin books under your slippage cap instead of sweeping four levels at once. We don't quote an average-improvement number yet; during beta every fill is measured against the naive alternative, so the proof comes from your own receipts.
Which venues are supported?+
Kalshi and Polymarket are both live today, behind one unified mkt_ ID scheme — so the same event maps across venues and adding the next venue won't change your integration. Coming: more venues, blocks, and financing against your positions.
Do you hold my funds?+
No. You keep your own wallet and exchange accounts — we never take custody of funds. We hold only an encrypted copy of your credentials, decrypted in memory only to sign the orders you (or your agent) submit.
Are my keys safe?+
Your Kalshi API key or Polymarket wallet key is envelope-encrypted with X25519 and decrypted only at the moment of signing an order. It is never written to logs and never returned by the API.
Can an AI agent trade for me?+
Yes. We host an MCP server at mcp.trymithril.com/mcp that exposes trading as agent tools — search_markets, place_order, cancel_order, get_portfolio, and more. Every action is capped by the same server-side risk limits, so an agent can trade without the ability to blow up the account.
What does an order look like?+
POST /v1/orders with subaccount_id, market_id, action, order_type, quantity, and price. You get back a risk-checked order with its status, and every fill is measured against the naive alternative for your execution receipt.
How much does it cost?+
Free during beta — no card, no trial clock. After beta: a few basis points on filled volume, only above a monthly notional threshold, so small size stays free. If the receipts don't show we save you more than we cost, don't pay us.
How do I get access?+
Book a call. The API and MCP server are live today, and we onboard every beta trader personally — 20 minutes to understand your flow, then keys the same day. We onboard a small group each week.
How does risk enforcement work?+
You set notional caps, per-market limits, slippage bounds, and a kill switch per subaccount. Every order is checked against them server-side before it reaches a venue — an order that breaches a limit is rejected, not forwarded.
Coming: more venues, blocks, and financing against your positions.
// TALK TO US
The proof will be
on your own flow.
Book 20 minutes with the founder — we'll look at your flow, set your limits, and get you keys the same day. A small group of beta traders is onboarded each week, free during beta.