Modeling 2026 US East Coast Statutory Tax Cliffs in OpenAPI 3.1 & MCP (NY LLC § 206, NYC CEMA § 255 & Estate Cliffs)

The East Corp Capital Open Data & API Desk has published OpenAPI 3.1.0 specifications and Model Context Protocol toolkits that encode 2026 East Coast statutory tax cliffs as piecewise-discontinuous functions for use by LLM agents. The work models New York's $7.16M estate tax exclusion, where exceeding 105% of the threshold retroactively eliminates the exemption, along with NYC CEMA mortgage recording tax under NY Tax Law § 255 and NY LLC Law § 206 publication costs, including a Certificate of Change move to Albany County that caps total costs at $215. The desk released vanilla JavaScript reference code covering the estate cliff and Medicare Part B IRMAA thresholds.

In algorithmic financial modeling, the most expensive engineering bugs do not stem from floating-point roundoff errors; they originate from treating statutory tax functions as continuous rather than piecewise discontinuous manifolds. Across the 16-state US East Coast corridor Maine to Florida , real-world state and municipal codes contain abrupt statutory cliffs where a single dollar of additional valuation or modified adjusted gross income MAGI triggers non-marginal, retroactive liability steps. At the East Corp Capital Open Data & API Desk https://eastcorpcapital.com/data-api/ , we standardize these state-level statutory discontinuities into machine-readable OpenAPI 3.1.0 specifications and Model Context Protocol MCP toolkits. Below is an engineering overview of how to model these non-linear structures cleanly in vanilla JavaScript and expose them across LLM agent architectures. A classic progressive income tax operates via marginal brackets: $$\text{Tax} x = \sum {i=1}^n \tau i \cdot \max 0, \min x - k {i-1}, k i - k {i-1} $$ Statutory cliffs, however, introduce step-function indicator multipliers $\mathbb{I} {x T}$: New York allows a basic exclusion amount of $7,160,000 in 2026. However, if the taxable estate exceeds 105% of this threshold $7,518,000 , the entire exemption is retroactively eliminated. At $7,160,001, marginal tax rates theoretically exceed 100%, creating an infamous financial trap modeled in our NY $7.16M Estate Tax Cliff & Santa Clause Calculator https://eastcorpcapital.com/calculators/ny-ma-estate-tax-cliff/ . Under NY Tax Law § 255, a Consolidation, Extension, and Modification Agreement CEMA allows a refinancer or property purchaser to pay Mortgage Recording Tax MRT only on the new money rather than the total principal. In NYC, where the combined MRT reaches 1.925% under $500k or 2.80% over $500k , failing to isolate statutory base credits costs borrowers tens of thousands of dollars. We quantify these exact spreads in the NYC Mansion Tax & CEMA § 255 Closing Cost Calculator https://eastcorpcapital.com/calculators/nyc-mansion-closing/ . Under NY LLC Law § 206, newly formed limited liability companies must publish notices in two designated county newspapers for six consecutive weeks. In New York County Manhattan , publisher rates and county clerk designations routinely exceed $1,400 to $1,650. Moving the registered office via Certificate of Change to Albany County caps total costs at $215 $25 state filing + $140 newspapers + $50 Certificate of Publication , an arbitrage detailed in our NY LLC Section 206 Albany Publication Arbitrage Calculator 2026 https://eastcorpcapital.com/calculators/ny-section-206-albany-llc-publication/ . Here is a production snippet modeling the 2026 NY Estate Cliff and Medicare Part B IRMAA cliff without external libraries: / Calculates 2026 NY Estate Tax Cliff under NY Tax Law § 952. Retroactive forfeiture occurs between 100% and 105% of exclusion. / function calculateNYEstateTax2026 estateValue { const EXCLUSION 2026 = 7160000; const CLIFF THRESHOLD = EXCLUSION 2026 1.05; // $7,518,000 if estateValue <= EXCLUSION 2026 { return { tax: 0, marginalTrap: false, taxableAmount: 0 }; } // The 105% Trap: Entire exclusion is revoked retroactively const isTrap = estateValue EXCLUSION 2026 && estateValue <= CLIFF THRESHOLD; const taxableBase = estateValue CLIFF THRESHOLD ? estateValue : estateValue - EXCLUSION 2026 ; // Progressive state brackets 5.06% to 16.0% const stateBrackets = { limit: 500000, rate: 0.0506 }, { limit: 1000000, rate: 0.055 }, { limit: 1500000, rate: 0.065 }, { limit: 2100000, rate: 0.080 }, { limit: 7100000, rate: 0.128 }, { limit: Infinity, rate: 0.160 } ; let accumulatedTax = 0; let remaining = isTrap ? estateValue : estateValue - EXCLUSION 2026 ; let previousLimit = 0; for const b of stateBrackets { const chunk = Math.min Math.max 0, remaining , b.limit - previousLimit ; accumulatedTax += chunk b.rate; remaining -= chunk; previousLimit = b.limit; if remaining <= 0 break; } return { tax: Math.round accumulatedTax , marginalTrap: isTrap, estateValue }; } A parallel step-function exists in federal health subsidies, calculated on our 2026 Medicare IRMAA MAGI Cliff & Form SSA-44 Calculator https://eastcorpcapital.com/calculators/medicare-irmaa-cliff-2026/ , where crossing tier thresholds by $1 triggers full-year surcharges. To make these calculations accessible to autonomous AI agents such as Claude, Cursor, and OpenAI tool runners , we publish: llms.txt openapi.json /.well-known/mcp.json Developers can inspect the complete corridor methodology across the Complete 60-Calculator East Coast Suite https://eastcorpcapital.com/calculators/ to integrate statutory accuracy directly into FinTech platforms.