Kalshi mispricing scan

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Create a new val, type = HTTP, paste this in, open the URL.\n//\n// Scans every open Kalshi market for ARITHMETIC mispricings -- sets of prices\n// that cannot all be right at once. It predicts nothing. Each check is an\n// identity that either holds or doesn't, so a flagged trade that fails to pay\n// is a bug in this file, not bad luck.\n\nconst FEE_COEF = 0.07;\nconst BASES = [\n \"https://api.elections.kalshi.com\",\n \"https://external-api.kalshi.com\",\n];\nconst MAX_PAGES = 6;\nconst PAGE_LIMIT = 200;\n// Sizes to price each opportunity at. Kalshi rounds its fee UP to the next\n// cent PER ORDER, so the same quote can be a loss at 1 contract and a profit\n// at 500. A single per-contract number would be meaningless.\nconst SIZES = [10, 100, 500];\nconst REFERENCE_SIZE = 100;\n// An EXHAUSTIVE set's YES prices must sum to about 100c -- some listed\n// outcome has to happen. A sum far below that is not a mispricing, it is\n// PROOF the set is not exhaustive: the market is pricing a large chance that\n// none of the listed outcomes occurs. \"What will be the 51st state\" summed to\n// 14c, meaning an ~86% chance of nothing happening; buying every YES there\n// loses the entire stake in the likely case. A genuine exhaustive-set arb\n// lands near 90-99c, so anything under this floor is discarded outright.\nconst EXHAUSTIVE_MIN_SUM = 0.85;\n\nconst ceilCents = (d) => Math.ceil(d * 100 - 1e-9) / 100;\n// Fee for ONE order of n contracts at price p.\nfunction orderFee(p, n) {\n if (p == null || !isFinite(p) || p <= 0 || p >= 1 || n <= 0) return null;\n return ceilCents(FEE_COEF * n * p * (1 - p));\n}\n\n// A quote within half a cent of 0 or 1 is almost always an unpopulated field,\n// not a real price. Left in, a spurious 0 would manufacture a huge fake arb.\nfunction px(cents, dollars) {\n const raw = dollars != null ? dollars : cents != null ? cents / 100 : null;\n if (raw == null) return null;\n const n = Number(raw);\n if (!isFinite(n)) return null;\n return n >= 0.005 && n <= 0.995 ? n : null;\n}\n\n// Price a set of legs at a given size. payoutPerContract is how many dollars\n// the whole basket is guaranteed to return per contract bought.\nfunction priceAt(legs, contracts, payoutPerContract) {\n let cost = 0, fees = 0;\n for (const l of legs) {\n cost += l.price * contracts;\n const f = orderFee(l.price, contracts);\n if (f == null) return null;\n fees += f;\n }\n const payout = payoutPerContract * contracts;\n return { cost, fees, payout, profit: payout - cost - fees, contracts };\n}\n\nfunction evaluate(legs, payoutPerContract) {\n const sized = SIZES.map((n) => priceAt(legs, n, payoutPerContract)).filter(\n Boolean,\n );\n if (!sized.length) return null;\n const ref = priceAt(legs, REFERENCE_SIZE, payoutPerContract);\n const best = sized[sized.length - 1];\n // Gross shortfall per contract, ignoring fees entirely -- shows whether the\n // book itself is tight or whether fees alone are the obstacle.\n const grossPerContract = payoutPerContract -\n legs.reduce((s, l) => s + l.price, 0);\n const profitable = sized.find((s) => s.profit > 0) || null;\n return {\n legs,\n sized,\n ref,\n best,\n grossPerContract,\n profitable,\n payoutPerContract,\n };\n}\n\nasync function fetchEvents() {\n let lastError = null;\n for (const base of BASES) {\n const out = [];\n let cursor = null, pages = 0, ok = false;\n try {\n while (pages < MAX_PAGES) {\n const url = base +\n \"/trade-api/v2/events?status=open&with_nested_markets=true&limit=\" +\n PAGE_LIMIT +\n (cursor ? \"&cursor=\" + encodeURIComponent(cursor) : \"\");\n const r = await fetch(url);\n if (!r.ok) throw new Error(\"HTTP \" + r.status);\n const j = await r.json();\n for (const e of j.events || []) out.push(e);\n ok = true;\n cursor = j.cursor;\n pages++;\n if (!cursor || !(j.events || []).length) break;\n }\n if (ok) return { events: out, pages, base, error: null };\n } catch (e) {\n lastError = String((e && e.message) || e);\n }\n }\n return {\n events: [],\n pages: 0,\n base: null,\n error: lastError || \"no Kalshi endpoint responded\",\n };\n}\n\nfunction analyse(events) {\n const found = []; // unconditional -- the money is there if depth is\n const conditional = []; // needs you to confirm the outcome list is complete\n const longshots = []; // rejected: low YES sum proves the set isn't exhaustive\n const shortfalls = []; // cents short of free, per contract, fees included\n let markets = 0, evs = 0, exclusive = 0, rejected = 0, checked = 0;\n\n for (const e of events) {\n const ms = e.markets || [];\n if (!ms.length) continue;\n evs++;\n const rows = ms.map((m) => {\n const yesAsk = px(m.yes_ask, m.yes_ask_dollars);\n const noAsk = px(m.no_ask, m.no_ask_dollars);\n if ((m.yes_ask != null || m.yes_ask_dollars != null) && yesAsk == null) {\n rejected++;\n }\n return {\n label: m.subtitle || m.yes_sub_title || m.ticker,\n ticker: m.ticker,\n yesAsk,\n noAsk,\n volume: m.volume ?? 0,\n oi: m.open_interest ?? 0,\n };\n });\n markets += rows.length;\n\n // --- Check 1: both sides of one market. Exactly one pays $1. -----------\n for (const r of rows) {\n if (r.yesAsk == null || r.noAsk == null) continue;\n checked++;\n const ev = evaluate(\n [{ side: \"YES\", label: r.label, price: r.yesAsk }, {\n side: \"NO\",\n label: r.label,\n price: r.noAsk,\n }],\n 1,\n );\n if (!ev) continue;\n if (ev.ref) shortfalls.push(-ev.ref.profit / ev.ref.contracts);\n if (ev.profitable) {\n found.push({\n ...ev,\n kind: \"Both sides of one market\",\n conditional: false,\n title: e.title || e.event_ticker,\n sub: r.label,\n volume: r.volume,\n oi: r.oi,\n });\n }\n }\n\n // --- Checks 2 & 3: exclusive multi-outcome sets ------------------------\n if (e.mutually_exclusive && rows.length >= 2) {\n exclusive++;\n const minVol = Math.min(...rows.map((r) => r.volume));\n const minOi = Math.min(...rows.map((r) => r.oi));\n\n if (rows.every((r) => r.yesAsk != null)) {\n checked++;\n const yesSum = rows.reduce((s2, r) => s2 + r.yesAsk, 0);\n const ev = evaluate(\n rows.map((r) => ({ side: \"YES\", label: r.label, price: r.yesAsk })),\n 1,\n );\n if (ev && ev.profitable) {\n if (yesSum >= EXHAUSTIVE_MIN_SUM) {\n conditional.push({\n ...ev,\n kind: \"Buy every outcome (YES)\",\n conditional: true,\n yesSum,\n title: e.title || e.event_ticker,\n sub: rows.length + \" outcomes\",\n volume: minVol,\n oi: minOi,\n });\n } else {\n // Not a finding at all. The low sum proves the set isn't exhaustive.\n longshots.push({\n title: e.title || e.event_ticker,\n legs: rows.length,\n yesSum,\n });\n }\n }\n }\n if (rows.every((r) => r.noAsk != null)) {\n checked++;\n const ev = evaluate(\n rows.map((r) => ({ side: \"NO\", label: r.label, price: r.noAsk })),\n rows.length - 1,\n );\n if (ev && ev.profitable) {\n found.push({\n ...ev,\n kind: \"Buy every outcome (NO)\",\n conditional: false,\n title: e.title || e.event_ticker,\n sub: rows.length + \" outcomes, at least \" + (rows.length - 1) +\n \" must pay\",\n volume: minVol,\n oi: minOi,\n });\n }\n }\n }\n }\n\n found.sort((a, b) => b.best.profit - a.best.profit);\n conditional.sort((a, b) => b.best.profit - a.best.profit);\n longshots.sort((a, b) => a.yesSum - b.yesSum);\n shortfalls.sort((a, b) => a - b);\n return {\n found,\n conditional,\n longshots,\n shortfalls,\n markets,\n evs,\n exclusive,\n rejected,\n checked,\n };\n}\n\nconst money = (d) => (d < 0 ? \"\\u2212$\" : \"$\") + Math.abs(d).toFixed(2);\nconst cts = (d) =>\n (d < 0 ? \"\\u2212\" : \"\") + Math.abs(d * 100).toFixed(2) + \"\\u00A2\";\nconst esc = (s) =>\n String(s).replace(\n /[&<>\"]/g,\n (m) => ({ \"&\": \"&\", \"<\": \"<\", \">\": \">\", '\"': \""\" }[m]),\n );\n\nexport default async function (req) {\n const t0 = Date.now();\n const { events, pages, base, error } = await fetchEvents();\n const a = analyse(events);\n const secs = ((Date.now() - t0) / 1000).toFixed(1);\n\n const tightest = a.shortfalls.length ? a.shortfalls[0] : null;\n const median = a.shortfalls.length\n ? a.shortfalls[Math.floor(a.shortfalls.length / 2)]\n : null;\n\n // Histogram of how far each book sits from free, in cents.\n const BUCKETS = [0, 2, 4, 6, 8, 12, 20, Infinity];\n const counts = new Array(BUCKETS.length - 1).fill(0);\n for (const s of a.shortfalls) {\n const c = s * 100;\n for (let i = 0; i < counts.length; i++) {\n if (c < BUCKETS[i + 1]) {\n counts[i]++;\n break;\n }\n }\n }\n const maxCount = Math.max(...counts, 1);\n\n // --- Rendering ------------------------------------------------------------\n // Every fragment is built as a plain variable with array joins and simple\n // concatenation. There are NO template literals nested inside other template\n // literals anywhere below. Nested backticks are what broke the last paste:\n // one dropped character mid-line left a template that never closed, and the\n // whole file failed to parse. Flat strings survive a bad paste far better\n // and fail in a way that's obvious to spot.\n const J = (arr) => arr.join(\"\");\n\n function legRow(l) {\n return '

' +\n '' + l.side +\n \"\" +\n '' + esc(l.label) + \"\" +\n '' + cts(l.price) + \"\" +\n \"

\";\n }\n\n function sizeRow(s) {\n return ' 0 ? \"win\" : \"lose\") + '\">' +\n '' + s.contracts + \"×\" +\n '' + money(s.cost) + \"\" +\n '' + money(s.fees) + \"\" +\n '' + money(s.payout) + \"\" +\n '' + money(s.profit) + \"\" +\n \"\";\n }\n\n function tradeCard(f, isCond) {\n const condBadge = f.conditional\n ? 'conditional'\n : \"\";\n const condWarn = isCond\n ? 'Pays nothing unless one of these ' + f.legs.length +\n \" outcomes actually occurs \\u2014 the \" + cts(f.yesSum) +\n \" sum implies roughly a \" +\n (100 - f.yesSum * 100).toFixed(0) + \"% chance none does.
\"\n : \"\";\n const turns = f.profitable\n ? \" Turns profitable at \" + f.profitable.contracts + \" contracts.\"\n : \"\";\n const depth = f.volume === 0\n ? ' No traded volume \\u2014 the quote may not be fillable at any size.'\n : \" Volume \" + f.volume.toLocaleString() + \", open interest \" +\n f.oi.toLocaleString() +\n \" \\u2014 neither is depth at the touch.\";\n return '

' +\n '

' + esc(f.kind) + \"\" +\n condBadge + \"

\" +\n '

' + esc(f.title) + \"

\" +\n '

' + esc(f.sub) + \"

\" +\n '

' + J(f.legs.map(legRow)) + \"

\" +\n '' +\n J(f.sized.map(sizeRow)) + \"

	cost	fees	returns	profit

\" +\n '

' + condWarn +\n \"Before fees the basket is \" + cts(f.grossPerContract) +\n \" from free per contract.\" +\n turns + depth + \"

\";\n }\n\n const verdictLine = a.found.length === 0\n ? \"No arbitrage\"\n : a.found.length +\n (a.found.length === 1 ? \" opportunity\" : \" opportunities\");\n\n let verdictSub = a.found.length === 0\n ? \"No set of prices checked is internally inconsistent once fees are counted. That's the expected result \\u2014 and a clean one, because this test can't produce false positives.\"\n : \"Best returns \" + money(a.found[0].best.profit) + \" on \" +\n a.found[0].best.contracts +\n \" contracts, guaranteed if the size is there. Check depth before acting \\u2014 a quote is not a fill.\";\n if (a.conditional.length) {\n verdictSub += \" \" + a.conditional.length + \" further basket\" +\n (a.conditional.length === 1 ? \" is\" : \"s are\") +\n \" listed below that require you to confirm the outcome list is complete \\u2014 those are bets, not arbitrage.\";\n }\n\n const foundSection = a.found.length\n ? '

Guaranteed \\u2014 the money is there if the depth is' +\n J(a.found.map(function (f) {\n return tradeCard(f, false);\n })) + \"

\"\n : \"\";\n\n const condSection = a.conditional.length\n ? '

Not guaranteed \\u2014 verify before believing' +\n '

These only pay if one of the listed outcomes actually happens. Their YES prices sum near 100\\u00A2, so the set might be exhaustive \\u2014 but Kalshi\\u2019s mutually_exclusive flag does not promise that, and if any unlisted outcome can occur you lose the whole stake. Read the event\\u2019s resolution rules before treating any of these as free money.

' +\n J(a.conditional.map(function (f) {\n return tradeCard(f, true);\n })) + \"

\"\n : \"\";\n\n function longshotRow(l) {\n return \"\" +\n '

' + esc(l.title) + \"

\" +\n '

' + l.legs + \" outcomes summing \" + cts(l.yesSum) +\n \" \\u2014 an implied \" + (100 - l.yesSum * 100).toFixed(0) +\n \"% chance none of them happens.

\" +\n \"excluded\";\n }\n const longshotSection = a.longshots.length\n ? '

Discarded longshot baskets' +\n '

Buying every YES here would have shown a large \\u201Cprofit\\u201D, but the prices sum far below 100\\u00A2 \\u2014 proof the set is not exhaustive. The market is pricing a high chance that none of the listed outcomes occurs, so the basket loses the entire stake in the likely case. Longshot bets wearing an arbitrage costume; excluded above.

' +\n '' + J(a.longshots.slice(0, 8).map(longshotRow)) +\n \"

\"\n : \"\";\n\n const tightLabel = tightest != null && tightest < 0\n ? \"Best \\u2014 past free by\"\n : \"Tightest \\u2014 short of free by\";\n const tightStyle = tightest != null && tightest < 0\n ? ' style=\"color:var(--up)\"'\n : \"\";\n const tightVal = tightest != null ? cts(Math.abs(tightest)) : \"\\u2014\";\n const medVal = median != null ? cts(median) : \"\\u2014\";\n\n const histBars = J(counts.map(function (c, i) {\n const hi = BUCKETS[i + 1] === Infinity ? \"\\u221E\" : BUCKETS[i + 1];\n const h = Math.max(3, (c / maxCount) * 100);\n return '

' +\n '

';\n }));\n const histLabels = J(\n BUCKETS.slice(0, -1).map(function (b, i) {\n return \"\" + (BUCKETS[i + 1] === Infinity ? b + \"+\" : b) + \"\";\n }),\n );\n\n const errBlock = error\n ? '

Couldn\\u2019t reach Kalshi: ' + esc(error) + \"

\"\n : \"\";\n\n const checksRows =\n '

Both sides of one market

Buy YES and NO on the same contract. Exactly one pays $1. Unconditional.

' +\n a.markets.toLocaleString() + \" markets\" +\n '

Buy every outcome, NO side

At most one outcome wins, so at least N\\u22121 of the NOs pay. Needs only exclusivity, which Kalshi states.

' +\n a.exclusive.toLocaleString() + \" sets\" +\n '

Buy every outcome, YES side

Pays only if a listed outcome actually happens. mutually_exclusive does not mean exhaustive. Flagged conditional, and discarded outright if the prices sum below ' +\n (EXHAUSTIVE_MIN_SUM * 100).toFixed(0) + \"\\u00A2.

\" +\n a.exclusive.toLocaleString() + \" sets\" +\n '

Quotes discarded

Prices within half a cent of 0 or 100 \\u2014 almost always an unpopulated field. Left in, they would invent enormous fake arbitrages.

' +\n a.rejected.toLocaleString() + \"\" +\n '

Not checked: depth

Whether any size is available at the quoted price. The gap most likely to turn a finding here into nothing.

\\u2014';\n\n const footText =\n \"Prices are asks \\u2014 what you\\u2019d pay to take. Fees are computed per order at each size using Kalshi\\u2019s round-up-to-the-cent rule, which is why the same quote can lose money at 10 contracts and make it at 500; \" +\n FEE_COEF +\n \" \\u00D7 contracts \\u00D7 P \\u00D7 (1\\u2212P) is their published shape but worth re-checking, since it alone decides whether a finding is real. \" +\n pages + \" page\" + (pages === 1 ? \"\" : \"s\") + \" fetched, capped at \" +\n MAX_PAGES +\n \", so this is a large sample of open markets rather than certainly all of them.\";\n\n const stamp = a.checked.toLocaleString() + \" checks \\u00B7 \" +\n a.markets.toLocaleString() +\n \" markets \\u00B7 \" + a.evs.toLocaleString() + \" events \\u00B7 \" + secs +\n \"s\";\n\n const body = errBlock +\n '

' +\n '

' + verdictLine + \"

\" +\n '

' + verdictSub + \"

\" +\n '

' + stamp + \"

\" +\n \"

\" +\n foundSection + condSection + longshotSection +\n '

How close does it get?' +\n '

' +\n '

' + tightLabel + '

\" + tightVal + \"

\" +\n '

Median \\u2014 short of free by

' +\n medVal + \"

\" +\n \"

\" +\n '

' + histBars + \"

\" +\n '

' + histLabels + \"

\" +\n '

Cents short of free per contract, fees included, across every two-sided check. The leftmost bucket includes anything at or past zero, i.e. the arbitrages above. At mid-range prices fees alone cost about 3.5\\u00A2, so the amber buckets are the only ones where fees could plausibly be the sole obstacle \\u2014 if the distribution sits well right of those, the books themselves are wide and no fee change would help.

' +\n \"

\" +\n '

What was checked' +\n checksRows + \"

\" +\n '

' + footText + \"

\";\n\n const html = \"\" + PAGE_HEAD + '

' +\n body + \"

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