ISO Week Number

ISO 8601 week numbers: date to week, week to date, weeks-per-year.

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What it can do

    What data it sees

    Do you need an account

    No: the server works without sign-in

    ISO 8601 week numbers: date to week, week to date, weeks-per-year.

    How to connect

    How to connect ISO Week Number to Claude

    The server address to paste into Claude settings:

    https://iso-week.gumballtools.com/api/mcp

    1. Open Claude (claude.ai or the desktop app).
    2. Go to Settings → Connectors.
    3. Click Add custom connector.
    4. Paste the server address copied below into Remote MCP server URL and click Add.
    5. In a chat, click + → Connectors and switch the new connector on.

    Custom connectors are available on Free, Pro, Max, Team and Enterprise plans (Free is limited to one). On Team and Enterprise an organization Owner adds the connector first under Organization settings → Connectors.

    Authorization

    After you click Add, a sign-in window for the service opens. Sign in with your own account and approve access. Claude never sees your password.

    How to connect ISO Week Number to ChatGPT

    The server address to paste into ChatGPT settings:

    https://iso-week.gumballtools.com/api/mcp

    1. Open ChatGPT in a browser (chatgpt.com). A Plus, Pro, Business, Enterprise or Edu plan is required.
    2. Turn on developer mode once: Settings → Apps → Advanced settings → Developer mode.
    3. Open Settings → Connectors and click Create.
    4. Fill in the form: Name (anything), Description (one line about what the service does), MCP server URL (copy it below).
    5. Under Authentication choose OAuth if the service requires sign-in, otherwise None. Click Create.
    6. In a new chat open + → Apps/Connectors and enable the connector.

    OpenAI has renamed this section before (Connectors → Apps/Plugins). If the label differs, search settings for "developer mode". On Business/Enterprise workspaces an admin must allow custom connectors first.

    Authorization

    On first use ChatGPT opens the service's sign-in window. Sign in and approve access.

    How to connect ISO Week Number to Cursor

    The server address to paste into Cursor settings:

    https://iso-week.gumballtools.com/api/mcp

    Fastest: click Open in Cursor below and confirm the prompt.

    Manually:

    1. In Cursor open Settings → Cursor Settings → MCP and click Add new global MCP server.
    2. Paste the JSON copied below into ~/.cursor/mcp.json (per project: .cursor/mcp.json in the repo root).
    3. Save the file. The server appears in the MCP list; authorize it there if asked.

    Authorization

    If the service needs sign-in, an authorize button appears next to the server in the MCP list.

    Server tool list (1)

    Raw names from tools/list. Only developers need these.

    runConverts between calendar dates and ISO 8601 week numbers, in either direction, and reports how many weeks an ISO year has. Use this whenever a date needs to be expressed as a week number, or a week number needs to be turned back into a date — sprint planning, report periods, "week 37" style scheduling, or reconciling two systems that disagree about what week it is. DO NOT compute this yourself with day-of-year divided by 7. ISO 8601 week 1 is defined as the week (Monday-Sunday) containing the year's first Thursday, not the week containing January 1st. This has two consequences that are easy to get wrong from memory: late-December dates can belong to ISO week 1 of the NEXT calendar year, and early-January dates can belong to ISO week 52 or 53 of the PREVIOUS calendar year. A year has 53 ISO weeks (not the usual 52) exactly when January 1 is a Thursday, or the year is a leap year and January 1 is a Wednesday — a rule nobody carries around, and getting it wrong produces a plausible-looking but incorrect week number with no visible sign of the error. Input is a single string, and the shape of the string picks the operation: "2027-01-01" a calendar date (YYYY-MM-DD) -> returns its ISO year, week, and weekday "2026-W53" an ISO week, no weekday given -> returns the Monday of that week "2026-W53-5" an ISO week and weekday (1-7, Mon-Sun) -> returns that exact date "2026" a bare 4-digit year -> returns whether it has 52 or 53 ISO weeks Refuses rather than guesses: slash-separated dates like "03/04/2025" are rejected as ambiguous (month/day vs day/month), two-digit years are rejected as a guess, invalid calendar dates (Feb 30) are rejected, and a week number beyond what that ISO year actually has (e.g. week 53 of a 52-week year) is rejected and told how many weeks that year has.