{
  "title": "Week number calculator",
  "human_url": "https://happytails.ai/en/date-time-tools/week-number-calculator/",
  "agent_url": "https://happytails.ai/agents/en/date-time-tools/week-number-calculator/",
  "language": "en",
  "markdown_url": "https://happytails.ai/en/date-time-tools/week-number-calculator.md",
  "content": "Week number calculator\nFind a date's ISO week number and week-year.\nHow can we improve this tool?\nReport a problem or share an idea.\nPlease leave out private information. Your message and the tool name go to our team via PostHog.\nHow to use Week number calculator\nEnter the values you want to calculate and choose the relevant units or settings.\nThe result updates as you type. Adjust the available settings if needed.\nReview the result, then use Copy result or a download link when available.\nUseful next steps\nDay of the week calculator\nBusiness days\nAdd days\nHow to use it\nChoose a calendar date. ISO weeks start on Monday, and the first week of the year contains January 4. The result also shows the ISO weekday, Monday 1 through Sunday 7.\nA worked example\nJanuary 1, 2021 belongs to ISO week 53 of 2020. January 4, 2021 starts ISO week 1 of 2021.\nWhat to know\nA date's calendar year can differ from its ISO week-year around New Year. This tool uses ISO 8601 week numbering, not Sunday-start calendars or organization-specific fiscal weeks.",
  "content_format": "text/plain",
  "visibility": "public",
  "links": [
    {
      "name": "Day of the week calculator",
      "url": "https://happytails.ai/en/date-time-tools/day-of-week-calculator/"
    },
    {
      "name": "Business days",
      "url": "https://happytails.ai/en/date-time-tools/business-days/"
    },
    {
      "name": "Add days",
      "url": "https://happytails.ai/en/date-time-tools/add-days/"
    }
  ],
  "tool": {
    "id": "week-number-calculator",
    "category": "date-time-tools",
    "built": true,
    "requirements": "A date's calendar year can differ from its ISO week-year around New Year. This tool uses ISO 8601 week numbering, not Sunday-start calendars or organization-specific fiscal weeks.",
    "implementation": {
      "fields": [
        {
          "key": "date",
          "label": "Calendar date",
          "value": "2026-10-06",
          "type": "date"
        }
      ],
      "input": false,
      "live": true,
      "presentation": "metrics",
      "note": "ISO 8601: weeks start on Monday; week 1 contains January 4. Dates near New Year can belong to the preceding or following ISO week-year.",
      "experience": {
        "automatic": true,
        "single": false,
        "inputMaxLength": 1000000,
        "inputMode": "text",
        "label": "Your text",
        "placeholder": "Type or paste your input…",
        "help": "Change the input or settings to update your result. Results update as you type. Up to 1,000,000 characters.",
        "action": null
      },
      "mode": "automatic",
      "interactive": false
    },
    "execution": "Browser interface",
    "api": null,
    "browser_agent": {
      "supported": true,
      "name": "run_current_tool",
      "discovery": "WebMCP on the human page in a supporting browser",
      "verification": "See audit/API-AUDIT.md; availability is not verification"
    }
  },
  "markdown": "# Week number calculator\n\n- Human page: https://happytails.ai/en/date-time-tools/week-number-calculator/\n- Markdown: https://happytails.ai/en/date-time-tools/week-number-calculator.md\n- Structured JSON: https://happytails.ai/agents/en/date-time-tools/week-number-calculator/index.json\n- Visibility: public\n\n## Tool capabilities\n\n| Property | Value |\n| --- | --- |\n| Tool ID | `week-number-calculator` |\n| Category | date-time-tools |\n| Implementation | Registered implementation. Registration alone is not a production-quality guarantee. |\n| Browser execution | Automatic updates after valid input or file selection. |\n| Browser processing | Browser; see tool notes for network behavior. |\n| HTTP API | Not callable through HTTP. |\n| Browser-agent interface | run_current_tool |\n\n### Implementation notes\n\nISO 8601: weeks start on Monday; week 1 contains January 4. Dates near New Year can belong to the preceding or following ISO week-year.\n\n### Inputs and settings\n\nNo free-text input is required. Use the file inputs and/or settings below.\n\n| Setting | Meaning | Control type | Default | Constraints |\n| --- | --- | --- | --- | --- |\n| `date` | Calendar date | date | \"2026-10-06\" |  |\n\n### Browser-agent workflow\n\n1. Open the human page in a browser that supports WebMCP.\n2. Discover the interface exposed by that page; use its actual schema.\n3. Select files on the page first when the tool requires files.\n4. Call `run_current_tool` with valid input and settings.\n5. Inspect the returned result or error and the displayed output. Retrieve files from the displayed download links.\n\nCalls do not automatically copy or download results. Browser permissions still apply. Interface availability alone is not proof of successful execution.\n\n### Planning specification\n\nA date's calendar year can differ from its ISO week-year around New Year. This tool uses ISO 8601 week numbering, not Sunday-start calendars or organization-specific fiscal weeks.\n\nThis describes intended requirements. Use the implementation notes, interface schema and observed output to determine current support.\n\n### Complete machine-readable capability record\n\n```json\n{\n  \"id\": \"week-number-calculator\",\n  \"category\": \"date-time-tools\",\n  \"built\": true,\n  \"requirements\": \"A date's calendar year can differ from its ISO week-year around New Year. This tool uses ISO 8601 week numbering, not Sunday-start calendars or organization-specific fiscal weeks.\",\n  \"implementation\": {\n    \"fields\": [\n      {\n        \"key\": \"date\",\n        \"label\": \"Calendar date\",\n        \"value\": \"2026-10-06\",\n        \"type\": \"date\"\n      }\n    ],\n    \"input\": false,\n    \"live\": true,\n    \"presentation\": \"metrics\",\n    \"note\": \"ISO 8601: weeks start on Monday; week 1 contains January 4. Dates near New Year can belong to the preceding or following ISO week-year.\",\n    \"experience\": {\n      \"automatic\": true,\n      \"single\": false,\n      \"inputMaxLength\": 1000000,\n      \"inputMode\": \"text\",\n      \"label\": \"Your text\",\n      \"placeholder\": \"Type or paste your input…\",\n      \"help\": \"Change the input or settings to update your result. Results update as you type. Up to 1,000,000 characters.\",\n      \"action\": null\n    },\n    \"mode\": \"automatic\",\n    \"interactive\": false\n  },\n  \"execution\": \"Browser interface\",\n  \"api\": null,\n  \"browser_agent\": {\n    \"supported\": true,\n    \"name\": \"run_current_tool\",\n    \"discovery\": \"WebMCP on the human page in a supporting browser\",\n    \"verification\": \"See audit/API-AUDIT.md; availability is not verification\"\n  }\n}\n```\n\n## Page guide\n\nFind a date's ISO week number and week-year.\n\nHow can we improve this tool?\n\nReport a problem or share an idea.\n\nPlease leave out private information. Your message and the tool name go to our team via PostHog.\n\n### How to use Week number calculator\n\n1. Enter the values you want to calculate and choose the relevant units or settings.\n2. The result updates as you type. Adjust the available settings if needed.\n3. Review the result, then use Copy result or a download link when available.\n\n## Useful next steps\n\n- [Day of the week calculator](https://happytails.ai/en/date-time-tools/day-of-week-calculator/) ([Markdown](https://happytails.ai/en/date-time-tools/day-of-week-calculator.md))\n\n- [Business days](https://happytails.ai/en/date-time-tools/business-days/) ([Markdown](https://happytails.ai/en/date-time-tools/business-days.md))\n\n- [Add days](https://happytails.ai/en/date-time-tools/add-days/) ([Markdown](https://happytails.ai/en/date-time-tools/add-days.md))\n\n## How to use it\n\nChoose a calendar date. ISO weeks start on Monday, and the first week of the year contains January 4. The result also shows the ISO weekday, Monday 1 through Sunday 7.\n\n### A worked example\n\nJanuary 1, 2021 belongs to ISO week 53 of 2020. January 4, 2021 starts ISO week 1 of 2021.\n\n### What to know\n\nA date's calendar year can differ from its ISO week-year around New Year. This tool uses ISO 8601 week numbering, not Sunday-start calendars or organization-specific fiscal weeks.\n"
}