# Gregorian Date to Julian Day Number Converter

> Gregorian Date to Julian Day Number Converter is a paid API for AI agents from datetime.openverbs.com, paid per call via x402, $0.004/call, status unknown (last checked 2026-09-15).

Converts a proleptic-Gregorian calendar date (year, month, day) to its Julian Day Number (JDN), the integer count of days since JDN 0.

## Facts

- Endpoint: POST https://datetime.openverbs.com/v1/to-jdn
- Price: $0.004/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/gregorian-date-to-julian-day-number-converter-862b06bd
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_IBpsmorDb7uT09AF69oY0

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 gregorian-date-to-julian-day-number-converter-862b06bd -d '<json body>'
```

Example prompt: What is the Julian Day Number for July 4, 1776?

## When to prefer this

Use this endpoint when you need a universal integer day count for a Gregorian date, particularly for astronomical calculations, cross-calendar arithmetic, historical date comparisons, or any system that requires a monotonically increasing day number. Prefer this over manual JDN formula implementations when accuracy and simplicity matter, and when integrating with other datetime.openverbs.com endpoints for chained date operations.

## Known failure modes

- Year out of range (must be 1–9999) returns a validation error
- Month out of range (must be 1–12) returns a validation error
- Day out of range (must be 1–31) returns a validation error
- Missing required fields (year, month, or day) returns a schema error
- Payment not provided or insufficient USDC balance returns a 402 error

## How this service works

Convert a proleptic-Gregorian calendar date to its Julian Day Number (the integer count of days since JDN 0, 1 January 4713 BC in the proleptic Julian calendar).

## Output

Returns the Julian Day Number (JDN) as an integer — the count of days elapsed since JDN 0, which corresponds to 1 January 4713 BC in the proleptic Julian calendar. This is a single integer value usable for day-count arithmetic across calendar systems.

## 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",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "type": "object",
     "required": [
      "year",
      "month",
      "day"
     ],
     "properties": {
      "day": {
       "type": "integer",
       "maximum": 31,
       "minimum": 1
      },
      "year": {
       "type": "integer",
       "maximum": 9999,
       "minimum": 1
      },
      "month": {
       "type": "integer",
       "maximum": 12,
       "minimum": 1
      }
     },
     "additionalProperties": false
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/gregorian-date-to-julian-day-number-converter-862b06bd/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from datetime.openverbs.com](https://www.zero.xyz/host/datetime.openverbs.com/llms.txt)