What day-count conventions does it support?
It supports seven conventions: 30/360, 30E/360, 30E/360 ISDA, ACT/360, ACT/365F, ACT/ACT ISDA, and ACT/ACT ICMA (with reference periods and stub decomposition).

@JayOfemi
Basic information
Provably correct day-count and accrued-interest calculations. A small, dependency-light TypeScript library and an MCP server, so an AI agent can get the exact number instead of guessing.
Add this server to your MCP-compatible client using the configuration below.
{
"mcpServers": {
"shikamaru": {
"command": "npx",
"args": [
"-y",
"--package=@jayofemi/shikamaru",
"shikamaru-mcp"
]
}
}
}Exact day-count fraction between two dates under a market convention. Dates are ISO YYYY-MM-DD. For ACT/ACT ICMA also pass frequency (coupons per year) and, for stub periods, the reference period boundaries. Deterministic; do not estimate this with a model.
Exact simple accrued interest (notional * rate * day-count fraction) between two dates. Dates are ISO YYYY-MM-DD; rate is the annual rate as a decimal (0.05 = 5%). Deterministic.
List the supported day-count conventions.
Whether a date is a business day under a holiday calendar, with the reason when it is not (weekend or holiday). Calendars are rules in code (no stale data feed). Deterministic; do not let a model guess market holidays.
Adjust a date to a business day under an ISDA convention and holiday calendar. Business days pass through unchanged. modified-following falls back to preceding rather than leave the month (the bond-market default). Deterministic.
Move a signed number of business days under a holiday calendar (settlement math: T+2 is count 2). Zero returns the date unchanged. Deterministic.
Generate coupon/payment accrual periods between an effective and a termination date: monthly to annual frequency, backward or forward roll, short or long stub, optional end-of-month rule, business-day adjustment per calendar. Returns each period's unadjusted and adjusted start and end. This is where hand-rolled date code goes wrong; do not approximate it.
List the supported holiday calendars with a one-line description of each.
Shikamaru is a small, dependency-light TypeScript library and MCP server that provides provably correct day-count, holiday-calendar, business-day, and payment-schedule calculations. It is designed for AI agents that need exact dates or numbers instead of guessing.
Install the npm package (npm install @jayofemi/shikamaru), then build and run the MCP server from source (npm run build && node dist/server.js) or launch it directly via npx @jayofemi/shikamaru. Any MCP client (Claude Desktop, IDE, etc.) can connect over stdio.
It supports seven conventions: 30/360, 30E/360, 30E/360 ISDA, ACT/360, ACT/365F, ACT/ACT ISDA, and ACT/ACT ICMA (with reference periods and stub decomposition).
Calendars are implemented as rules in code plus a pinned table of historical one-off closures. A scheduled CI run checks every calendar against the latest QuantLib weekly to detect drift.
The server requires Node.js and npm. It is a dependency-light TypeScript package with no external data feeds.
The library tests against published reference vectors (ISDA worked examples, official holiday lists) and differential batteries against QuantLib. CI regenerates these batteries from the latest QuantLib on every push and weekly.
Use the official MCP Inspector: after building, run `npx @modelcontextprotocol/inspector node dist/server.js`. It opens a local UI that lists tools and allows calling them, e.g., `day_count_fraction` with start `2003-11-01`, end `2004-05-01`, convention `ACT/ACT ISDA` returns about 0.4977.

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