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Timezone Truth

by gumballtools.com · remote · no sign-in to list tools · v0.1.0 · published by com.gumballtools

Convert times between IANA zones and detect skipped or ambiguous DST local times.

Final · 1
CompareRegistry entry

1 tool: 1 do something that can't be undone.

Scanned Oct 21, 2026

1 check matched something in the tool definitions. No finding is not a safety guarantee. How the checks work.

claude mcp add --transport http timezone-truth https://timezone-truth.gumballtools.com/api/mcp

Findings

Matches of fixed checks, with the text they matched.

1 warn
  • Warnconvert_time

    The server marks "convert_time" read-only (readOnlyHint: true), and its own name, description or input give the class "irreversible".

    Matched text

    annotations: {"readOnlyHint":true,"openWorldHint":false}; The name "convert_time" says "convert": a word for a change.

    What this check looks for

Tools

Open a tool for its reasons and full description. Descriptions are the publisher's own words, shown as they are.

1 tool

Can't be undone 1Claude Code: ask
  • convert_timeConvert a wall-clock time between two IANA timezones, and report the ways the conversion can be wrong.1 finding

    Why it is in this group

    • The name "convert_time" says "convert": a word for a change.
    • The input addresses people (input.to): what it sends cannot be taken back.
    • The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.

    Findings

    • Warn

      The server marks "convert_time" read-only (readOnlyHint: true), and its own name, description or input give the class "irreversible".

      Matched text

      annotations: {"readOnlyHint":true,"openWorldHint":false}; The name "convert_time" says "convert": a word for a change.

      What this check looks for
    Description, as the server wrote it
    Convert a wall-clock time between two IANA timezones, and report the ways the conversion can be wrong. ALWAYS use this instead of doing the arithmetic. Timezone conversion looks like addition and is not: the mapping from a local time to an instant is not a function. - On the spring-forward date, an hour of local time DOES NOT EXIST. Asked to convert 02:30 on that date, a model will return a plausible timestamp for a time that never happens. This tool returns null and says why. - On the fall-back date, an hour happens TWICE. There are two correct answers an hour apart; this returns both rather than silently choosing. - The gap between two zones is not constant. Zones start and end daylight saving on different dates, so a cached offset is wrong for weeks each year. - Not all offsets are whole hours: India is +05:30, Nepal +05:45. Input: `time` must be YYYY-MM-DD HH:MM (or with T, and optional seconds) — free-form dates are refused rather than guessed. `from` and `to` must be full IANA names such as "America/New_York". ABBREVIATIONS ARE REJECTED, deliberately, even though most runtimes accept them. Node resolves "BST" to Bangladesh Standard Time (UTC+06:00) when nearly everyone writing it means British Summer Time (UTC+01:00) — a five-hour error that yields a perfectly plausible timestamp. Same for CST, IST, PST, and EST. Returns: the chosen UTC instant (null if the local time does not exist), every candidate instant, both zone readings with the offset and abbreviation that applied on THAT date, the difference between the zones, upcoming clock changes for both, and warnings. Check `warnings` for severity "error" before using the result.

    Annotations the server declares

    • readOnlyHint: true
    • openWorldHint: false

This is not a safety rating, and no finding is not a safety guarantee. The groups and findings come from fixed checks of the tool definitions the server returned on the date shown, not from its code or what it does when called. How the checks work.

Install

Pinned to version 0.1.0. Values in angle brackets are yours to fill in.

claude mcp add --transport http timezone-truth https://timezone-truth.gumballtools.com/api/mcp

Run in a terminal.

Claude Code permissions

Allow the reads, ask before a change, deny the deletes. Paste into .claude/settings.json.

.claude/settings.json
{
  "permissions": {
    "allow": [],
    "ask": [
      "mcp__timezone-truth__convert_time"
    ],
    "deny": []
  }
}

Tools that only read are allowed, tools that change things ask first, tools that delete or cancel are denied. It assumes the server is installed as timezone-truth. Review it before you use it.