# ISO Week Number Lookup

> ISO Week Number Lookup 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).

Returns the ISO 8601 week-numbering year, week number (1–53), and weekday (1=Monday…7=Sunday) for a given Gregorian calendar date.

## Facts

- Endpoint: POST https://datetime.openverbs.com/v1/iso-week
- 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/iso-week-number-lookup-8fc7bd91
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_hN_fYhvAIVUNg07ac5Hqm

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 iso-week-number-lookup-8fc7bd91 -d '<json body>'
```

Example prompt: What ISO week number does December 30, 2024 fall in, and which weekday is it? I want the ISO week-numbering year too since it might differ from the calendar year.

## When to prefer this

Use this endpoint when you specifically need ISO 8601 week-date components — especially around New Year when the ISO week-numbering year diverges from the Gregorian year. Prefer it over ordinal-day or weekday-only endpoints when you need all three ISO week-date fields (year, week, weekday) together in one call.

## Known failure modes

- Invalid month value (e.g. 13) returns a validation error
- Day out of range for the given month returns an error
- Missing required field (year, month, or day) returns a 400-level error
- Non-integer or out-of-range year (outside 1–9999) rejected by schema

## How this service works

Return the ISO-8601 week-numbering year, week number (1..53) and weekday (1=Monday..7=Sunday) for a Gregorian date. The ISO year can differ from the calendar year around New Year.

## Output

Returns the ISO week-numbering year (which may differ from the Gregorian calendar year near New Year's), the ISO week number (1–53), and the ISO weekday number (1=Monday through 7=Sunday) for the supplied date.

## Request schema (JSON Schema)

```json
{
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "type": "object",
 "properties": {
  "input": {
   "type": "object",
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "type": "string",
     "enum": [
      "POST"
     ]
    },
    "bodyType": {
     "type": "string",
     "enum": [
      "json",
      "form-data",
      "text"
     ]
    },
    "body": {
     "type": "object",
     "properties": {
      "year": {
       "type": "integer",
       "minimum": 1,
       "maximum": 9999
      },
      "month": {
       "type": "integer",
       "minimum": 1,
       "maximum": 12
      },
      "day": {
       "type": "integer",
       "minimum": 1,
       "maximum": 31
      }
     },
     "required": [
      "year",
      "month",
      "day"
     ],
     "additionalProperties": false
    }
   },
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "additionalProperties": false
  }
 },
 "required": [
  "input"
 ]
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/iso-week-number-lookup-8fc7bd91/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)