# Calendar Systems – Gregorian / Julian Date Converter

> Calendar Systems – Gregorian / Julian Date Converter is a paid API for AI agents from calendar-systems.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-29).

Converts a date between the Gregorian (New Style) and Julian (Old Style) calendar systems, returning both dates and the day difference between them.

## Facts

- Endpoint: GET https://calendar-systems.x402tookit.com/julian-calendar?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/calendar-systems-gregorian-julian-date-converter-346ec136
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_EHF6j7_TsjZr-LIg8LDum

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability calendar-systems-gregorian-julian-date-converter-346ec136
```

Example prompt: What is the Julian (Old Style) calendar date for October 15, 1582 Gregorian, and how many days apart are the two calendars on that date?

## When to prefer this

Choose this endpoint when you need to programmatically convert a specific date between the Gregorian and Julian calendar systems, especially for historical research, document dating, liturgical calendar cross-referencing, or any scenario where Old Style / New Style date reconciliation is required. It is purpose-built for this single conversion and returns the day difference directly, making it more reliable than general-purpose date libraries that may not handle pre-reform dates correctly.

## Known failure modes

- Invalid date format (not YYYY-MM-DD) — returns error or null fields
- Date outside supported range (year 1–9999) — returns error
- Invalid 'from' enum value other than 'gregorian' or 'julian' — returns error
- Missing required 'date' query parameter — returns validation error

## How this service works

Convert between Gregorian and Julian calendar dates (Old Style / New Style) with the day difference for that date.

## Output

Returns the input date expressed in both the Gregorian and Julian calendars (YYYY-MM-DD strings), the integer day difference between the two systems for that date, the weekday name, and a boolean indicating whether the date falls before the 1582 Gregorian reform, along with optional summary and disclaimer fields.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "date"
     ],
     "properties": {
      "date": {
       "type": "string",
       "description": "YYYY-MM-DD, year 1 to 9999"
      },
      "from": {
       "enum": [
        "gregorian",
        "julian"
       ],
       "type": "string",
       "description": "gregorian (default) or julian: the calendar the date is written in"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "from": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "weekday": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
      },
      "julianDate": {
       "type": [
        "null",
        "string"
       ]
      },
      "notChecked": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "dayDifference": {
       "type": [
        "null",
        "number"
       ]
      },
      "gregorianDate": {
       "type": [
        "null",
        "string"
       ]
      },
      "before1582Reform": {
       "type": [
        "boolean",
        "null"
       ]
      }
     }
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/calendar-systems-gregorian-julian-date-converter-346ec136/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from calendar-systems.x402tookit.com](https://www.zero.xyz/host/calendar-systems.x402tookit.com/llms.txt)