Julian Date Converter: Calendar Date and Time to Julian Day (USNO)

usno/julian-date-convert

Converts a calendar date and a time of day (Universal Time) to its Julian date, the continuous day count used in astronomy, as computed by the U.S. Naval Observatory. Returns the Julian date as a string with six decimals, with the era and the date and time as understood. Astronomical computation data passed through unmodified and served by Eden Engine; not an official U.S. Naval Observatory product.

activeper callv1

Price

$0.0026 per call

You pay the price shown. If a call turns out to cost more than its quote, you pay the actual price, capped at twice the quote. No monthly minimum. Top-ups start at $5.

Data source

U.S. Naval Observatory

Data from the U.S. Naval Observatory (USNO), U.S. Department of the Navy, a US federal government work in the public domain (17 USC 105); no credit is required. Served by Eden Engine; not an official U.S. Naval Observatory product.

Use it

Five steps: search, inspect, learn, run, settle. No per-tool setup; your agent reaches this tool through the meta-tools it already has.

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agent

// 1. search: find the tool
omnial_search({ query: "what you need" })

// 2. inspect: price and input schema
omnial_inspect({ tool: "usno/julian-date-convert" })

// 3. learn: read the usage guide at runtime
omnial_learn({ tool: "usno/julian-date-convert" })

// 4. run: price the exact call first, then run it
omnial_execute({ tool: "usno/julian-date-convert", input: { /* see input_schema */ }, dry_run: true })
omnial_execute({ tool: "usno/julian-date-convert", input: { /* ... */ } })

// 5. settle: the call is charged when it finishes, nothing to do

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Pricing

Every charge this tool can incur.

Charge	Price
Per call	$0.0026

Updated: Oct 20, 2026

Input and output schemas

Input schema

input_schema.json

{
  "type": "object",
  "required": [
    "date"
  ],
  "properties": {
    "date": {
      "type": "string",
      "pattern": "^[0-9]{1,4}-(0?[1-9]|1[0-2])-(0?[1-9]|[12][0-9]|3[01])$",
      "description": "Calendar date as YYYY-MM-DD, for example 2026-10-19 (leading zeros on month and day are optional). The service refuses dates it does not support."
    },
    "time": {
      "type": "string",
      "default": "00:00",
      "pattern": "^([01][0-9]|2[0-3]):[0-5][0-9](:[0-5][0-9](\\.[0-9]{1,6})?)?$",
      "description": "Time of day in Universal Time, 24-hour hh:mm, optionally hh:mm:ss or hh:mm:ss.ffffff (two-digit hour, minute and second). Defaults to 00:00, midnight at the start of the date."
    }
  },
  "additionalProperties": false
}

Output schema

output_schema.json

{
  "type": "object",
  "required": [
    "data"
  ],
  "properties": {
    "data": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "jd": {
            "type": "string",
            "description": "The Julian date, a string with six decimals, for example 2461333.000000."
          },
          "tz": {
            "type": "number",
            "description": "Time zone offset, 0 meaning Universal Time."
          },
          "day": {
            "type": "integer"
          },
          "era": {
            "type": "string",
            "description": "AD or BC."
          },
          "time": {
            "type": "string",
            "description": "The time as understood by the service, hh:mm:ss.s."
          },
          "year": {
            "type": "integer"
          },
          "month": {
            "type": "integer"
          }
        },
        "additionalProperties": true
      },
      "description": "One entry holding the conversion."
    },
    "apiversion": {
      "type": "string",
      "description": "USNO API version that produced the data."
    }
  },
  "description": "The USNO Julian date response.",
  "additionalProperties": true
}