Julian Day Conversion for AI Agents

Overview

Dates are converted with the standard integer algorithm for the proleptic Gregorian calendar: the Gregorian rules are applied to every year, including years before 1582, and no switch to the Julian calendar is made. `julianDayNumber` is the integer JDN of the given date, which by astronomical convention labels the day beginning at noon UT, so 2024-03-15 is 2460385. The reverse direction uses the matching inverse algorithm and also returns `year`, `month` and `day` as separate numbers.

`modifiedJulianDate` is calculated as JDN minus 2400000.5, so it always ends in .5 and corresponds to noon UT on that date; subtract 0.5 more for the MJD at midnight. `dayOfWeek` is taken from JDN modulo 7, with JDN 0 being a Monday.

`weekNumber` is the ISO 8601 week, where weeks start on Monday and week 1 contains the year's first Thursday, so dates in early January can fall in week 52 or 53 of the previous year. `dayOfYear` runs from 1 to 366. Years 0 to 99 are handled as those years rather than as 1900 to 1999. `daysFromToday` is the JDN minus today's JDN by the server's clock, negative for past dates; it is null on the Free plan. Send either `date` in `YYYY-MM-DD` form or `jdn` as an integer; when both are present, `date` is used.

Live Test Julian Day Conversion for AI Agents Source →

The tool

Once your client is connected to the VerveContext server, this appears in its tool list as JulianDayConversionforAIAgents. It is read-only and open-world — it fetches and never mutates anything on your side — so most clients call it without asking you to confirm.

{
  "name": "JulianDayConversionforAIAgents",
  "arguments": {
    "date": "2024-03-15"
  }
}

You do not name the tool yourself; the model picks it. Asking about 2024-03-15 in the terms this source covers is enough for it to reach for JulianDayConversionforAIAgents on its own — naming it explicitly also works, and is the way to force the call.

Connecting

One server URL covers every source in the catalog, including this one. Authorization is OAuth: the client opens a browser once, and there is no key to paste into a config file.

{
  "mcpServers": {
    "vervecontext": {
      "url": "https://api.vervecontext.com/v1/mcp"
    }
  }
}

https://api.vervecontext.com/v1/mcp

Per-client setup — Claude, Cursor, VS Code, ChatGPT — is on the MCP setup page.

Arguments

These are the properties on the tool's inputSchema, so a well-behaved client validates them before the call is made. Premium arguments are accepted on every plan but only take effect on plans that include them.

What the model gets back

The result carries a structuredContent object matching the tool's declared outputSchema, so a client reads fields without parsing prose. status is "ok" and error is null on success; a null field means the value was not available for that input, not that the call failed.

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{
  "status": "ok",
  "error": null,
  "data": {
    "gregorian": "2024-03-15",
    "julianDayNumber": 2460385,
    "modifiedJulianDate": 60384.5,
    "dayOfWeek": "Friday",
    "weekNumber": 11,
    "dayOfYear": 75,
    "daysFromToday": -340
  }
}

Response fields

Paths are relative to data. Premium fields are absent rather than zeroed on plans that do not include them, so check for presence instead of comparing to 0.

Why ground on it

A model can produce something that looks like this answer from its training data, and be confidently out of date or simply wrong. This source returns the current value in a shape you can check, which is the difference between an answer you can cite and one you have to hedge.

Point an evaluation at gregorian: it is the field most worth pinning a claim to, and it is either present and current or absent — never plausibly invented.

Failure modes

Errors come back as tool errors carrying a sentence the model can act on, not a bare status code. Error handling covers the full list.

A call costs 1 credit each time the tool actually runs; a model that reasons about the tool without calling it costs nothing.

Use cases

Astronomical Software

Calculate precise day numbers for celestial events

Historical Research

Convert historical dates to a unified day count

Date Arithmetic

Calculate day differences across long time spans

Scientific Applications

Use continuous day counts for time series data

Other ways to use Julian Day Conversion for AI Agents

Set up Julian Day Conversion for AI Agents on VerveContext, or reach the same source a different way. Your VerveContext account and credits work on all of them — one key, one balance.

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