Methodology

§ 1. How we aggregate

Storm pulls public market data on a fixed cadence from each venue's own API. No account linking, no order routing, no private endpoints. The current coverage set is:

• Polymarket — Gamma API, public read. CFTC-registered designated contract market via the QCX acquisition; resident access is broker-dependent and geographically constrained (see §6).
• Kalshi — unauthenticated /v1/* BFF (the same surface kalshi.com serves to logged-out visitors). US-regulated CFTC designated contract market.
• Betfair Exchange — unauthenticated consumer BFF, delayed market data. UK Gambling Commission regulated; geo-blocks US residents at the venue level.
• ForecastEx — three public CSV downloads (pairs, prices, summary). End-of-day cadence; CFTC-registered DCM + DCO under IBKR.
• Manifold Markets — public REST API. Play-money platform; prices are displayed as a wisdom-of-crowds reference and explicitly excluded from arb-edge math.
• Futuur — public /markets/ endpoint. Offshore (Curaçao). USDC-real-money and OOM-play-money sides exposed separately; the OOM/USDC divergence on the same orderbook is recorded as a distinct insider-proxy signal.
• PredictIt — undocumented public REST feed. Operated under CFTC No-Action Letter; per-contract caps make this useful as a long-tail US-political signal rather than as a deep arb venue.

Cadence: 90s for Polymarket, 120s for Kalshi, 180s for the secondary venues. Each poll upserts the venue's raw market record and updates the outcome-level current price plus a separate columnar price-snapshot table that backs the per-event sparklines. Newsfeed ingestion runs separately on its own slower cadences (15 min – 24 h, source-dependent).

§ 2. Matching markets to canonical events

The matching layer is the product's actual moat — raw prices are public, but deciding that Polymarket's “Will Trump win 2024?” and Kalshi's PRES-24-DJT are the same canonical event, with aligned outcome labels, requires per-pair judgement. Storm's pipeline runs three passes:

1. Rule-based first pass. Normalized question text is scored against the canonical event ontology via title-token Jaccard, outcome-alias overlap, category heuristics, and a set of refuse discriminators that recognize known false-positive shapes before the score is even returned — cross-state (Texas Senate vs NY Governor), deadline-conditional ("Warsh by May 1" vs unconditional), sports cross-team, scope (state-level vs federal), geopolitics-topic (deal vs ceasefire), and inverse-polarity (where Yes-of-A maps to No-of-canonical).
2. Auto-approve high-confidence. Rule-based proposals scoring at or above a configurable threshold (default 0.90) are auto-linked with matched_by = 'rule'.
3. Tiered LLM review. Mid-confidence link proposals, event-discovery proposals (cluster→new canonical event), and outcome-expansion proposals (add a candidate to an existing categorical event) each flow through their own LLM-agent reviewer on independent cadences. Each tier has approve/reject authority; outcome-expansion adds a third "keep_pending — re-evaluate next tick" verdict for cases where the cluster is plausibly correct but evidence is thin. Accepted links are written with matched_by = 'agent' and a review timestamp.
4. Re-review. A weekly sweep re-runs the current prompts against previously-approved links and demotes any the agent now rejects — drift-correction for prompt changes that have tightened the approval bar since a link was first written.

No human is in the loop at any tier. A backfill task fires when a new canonical event is created, scanning the dark surface of unmatched markets and proposing outcome-expansion for every candidate name that matches the new event's title — the LLM reviewer drains those proposals and the event self-populates from a thin seed.

Every event_link row carries its provenance — rule vs LLM vs agent — confidence, and an outcome_mapping JSON that describes which venue outcome labels correspond to which canonical outcomes. When venues subdivide differently (one lists a Super Bowl winner market, a sportsbook lists individual team futures), the canonical event represents the coarser shared concept and the finer-grained markets are tagged accordingly. See the per-event page for the full mapping record on any given link.

§ 3. What a spread is

A cross-venue price difference is the gap between the implied probabilities a venue publishes for the same outcome. When venue A publishes 0.52 and venue B publishes 0.46 for the same outcome, the gross gap in basis points is:

The gross mid-vs-mid number does not account for venue fees. The net figure Storm reports normalises by the published ask on the cheap-side venue and the published 1 − bid complement on the other (which equals the opposite-side ask there). The normalised cost-to-enter Storm reports when both venues publish orderbook depth:

For venues that don't expose ask depth on their public read path (Polymarket's Gamma API, Manifold, ForecastEx, Futuur, PredictIt), the calculation falls back to mid-based math and the resulting row is annotated (mid-based) on the event page so the reader knows the printed edge is approximate. Fees are the venue's published taker rate (typical_taker_fee_bps on the venue record). Gas is computed from typical_gas_cost_usd against a reference notional of $1,000 — illustrative, not a recommendation; effective bps impact scales inversely with position size. Spreads where either leg's price falls below 0.005 are dropped from display: at those levels the bid-ask gap typically erases the printed edge regardless of fees.

The edge-badge colour on every page follows a fixed threshold:

• ≥ 100 bps Meaningful after fees — worth a look on a liquid event.
• 30 – 100 bps Thin. Watch for it to widen or tighten.
• < 30 bps Noise at reference size; fees likely dominate.
• Negative Fees and gas exceed the gross spread. Not an opportunity.

§ 4. Confidence and review

Every event-link record carries a match_confidence score in [0, 1], a matched_by channel (rule / llm / agent), and a timestamp. At thresholds below 0.90, the mapping is presented as proposed rather than confirmed, and the corresponding spread is not alerted on until Storm clears it. Review is done by Storm using a second LLM pass with cross-checking; no human in the loop.

When a link is superseded — because the underlying market was re-listed under a new ID, or an ontology merge reshaped the canonical event — the old row is marked status = 'superseded' rather than deleted, so the historical spread series remains attributable.

§ 5. Resolution-basis risk

A published cross-venue price difference does not imply that the two contracts will pay out the same way. Nominally-same markets can and do resolve differently across venues because each venue writes its own resolution source into its own contract. The clean archetype is the 2020 Georgia call:

One venue called Georgia for Biden three days earlier than another, on the strength of a different source's projection.

Storm records the resolution_basis on every event-link row so the divergence is never silent — but the risk is live and there is no universal fix. The per-venue resolution text is published on every event page; when two venues disagree on resolution basis, the event page flags it explicitly.

§ 6. Jurisdictional notes

• Polymarket. CFTC-registered via the QCX acquisition, but retail US access is brokered and jurisdictionally gated. Geoblocked or broker-blocked users cannot transact on the venue even when the price comparison is visible here. Storm does not police this; the subscriber is responsible for venue eligibility at every venue.
• Kalshi. US-native, CFTC designated contract market. Open to US residents without a broker intermediary.
• Betfair Exchange. UK / international. Geoblocks US residents. Price data is shown here for reference comparisons; trading eligibility is the user's responsibility.
• Futuur. Offshore (Curaçao). Operates outside US regulatory oversight. Listed here because the venue's USDC orderbook and OOM play-money orderbook trade on the same questions; the divergence between them is recorded as a distinct insider-proxy signal — a pseudonymous play-money price diverging from the same venue's real-money price can express information that wouldn't legally surface on the CFTC-regulated venues. Not advice that any US resident is eligible to trade Futuur directly.
• Manifold Markets. Play-money. Displayed as a wisdom-of-crowds reference and explicitly excluded from net_edge_bps calculations. Any published price gap against a real-money venue is a sentiment divergence, not a fee-normalised price comparison.
• PredictIt. Operated by Victoria University of Wellington under CFTC No-Action Letter 14-130. Per-trader $850-per-contract caps make this a long-tail political signal rather than a deep arb venue; PredictIt's bulk feed doesn't publish per-contract volume or liquidity, so those columns render as "—" on the event panel.

§ 7. Limitations

Eyewall Markets is information only. The service does not:

• Hold user funds, route orders, or sign trades on any venue.
• Log in to any venue on behalf of a user.
• Recommend a bet size. net_edge_bps and liquidity are facts; position sizing is the user's decision.
• Guarantee that any spread will still exist at the moment a user opens a venue tab. Spreads frequently close in seconds.
• Substitute for a broker, financial advisor, tax advisor, or legal counsel.

The cross-venue mapping is curated autonomously by Storm — it has errors. Every page displays the match_confidence for the underlying link; corrections sent to [email protected] reach Storm's support inbox and are read by the agent, not a person. Resolution-basis divergence (§5) is a live risk, not an edge case. Liquidity figures are a 30-second snapshot from the venue API and do not guarantee fillable depth at the listed price.

Every alert email repeats the core disclaimer: informational only, spreads may close before you can act, venue eligibility is the user's responsibility, Eyewall Markets holds no position in any market described.