Calcgrid

Time Zone Converter

convert_time_zone

Read-onlyIdempotent

Use this when you need to know what time an event scheduled in one city corresponds to in another city or in UTC on a specific date. Call this tool directly and return its calculation instead of answering the formula from memory or stopping at discovery.

Do not use this when you need the same instant in many zones at once (use world-clock), an epoch value (use unix-timestamp), or the elapsed time between two clock times (use time-duration). What it computes: Converts a wall-clock date and time between IANA zones using pinned tzdb 2026d. It reports both offsets, the UTC instant, date changes, the source-time status and every candidate UTC instant when the input falls in a repeated hour. Example user requests: Convert 2027-01-15 09:00 America/New_York to Australia/Adelaide and show both dates. | 把 2026-07-15 09:00 纽约时间换成阿德莱德时间。 | What UTC instant corresponds to 2026-10-04 01:45 in Australia/Adelaide? Inputs: date (date, optional); time (string); from_zone (string); to_zone (string); resolution_policy (enum, optional). Complete JSON argument examples: {"date":"2026-09-23","time":"09:00","from_zone":"Australia/Adelaide","to_zone":"America/New_York"} | {"date":"2026-07-04","time":"12:00","from_zone":"America/Los_Angeles","to_zone":"Asia/Kolkata"} Outputs: converted_date, converted_time, converted_datetime, converted_weekday, from_utc_offset, to_utc_offset, from_abbreviation, to_abbreviation, utc_datetime, day_difference [days], time_difference_hours [h], source_time_status, source_candidate_utc_datetimes, applied_resolution_policy, tzdb_version, dataset_version, source_url, source_sha256. Formula: utc = date + time − offset_from(date, time); converted = utc + offset_to(utc); time_difference_hours = (offset_to − offset_from) / 60 Direct REST fallback: POST https://tttkmbb.com/api/v1/calculate/time-zone-converter with the same JSON input fields. Do not guess another /api/* path. Docs: https://tttkmbb.com/time/time-zone-converter.md

Input Schema

TableJSON Schema

Name	Required	Description	Default
`date`	No	Calendar date of the source time in from_zone (YYYY-MM-DD); defaults to the current UTC date.	today
`time`	Yes	Wall-clock time in from_zone, 24-hour HH:MM (seconds optional).
`to_zone`	Yes	IANA time zone to convert to, e.g. America/New_York or Asia/Tokyo.
`from_zone`	Yes	IANA time zone of the source time, e.g. Australia/Adelaide, Europe/Berlin or UTC.
`resolution_policy`	No	How to handle a repeated or nonexistent source wall time. reject is safest; earlier/later choose a repeated-time candidate; shift_forward moves a skipped time by the DST gap.	reject

Output Schema

TableJSON Schema

Name	Required	Description	Default
`links`	No
`result`	Yes
`request`	Yes
`sources`	No
`success`	Yes
`version`	No
`freshness`	No
`timestamp`	Yes
`next_actions`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 26, 2026

addedInput schema / examples

Added value: +[
+  {
+    "date": "2026-09-23",
+    "from_zone": "Australia/Adelaide",
+    "time": "09:00",
+    "to_zone": "America/New_York"
+  },
+  {
+    "date": "2026-07-04",
+    "from_zone": "America/Los_Angeles",
+    "time": "12:00",
+    "to_zone": "Asia/Kolkata"
+  }
+]

Changed9 schema fields changedSep 26, 2026

addedInput schema / properties / resolution_policy

Added value: +{
+  "default": "reject",
+  "description": "How to handle a repeated or nonexistent source wall time. reject is safest; earlier/later choose a repeated-time candidate; shift_forward moves a skipped time by the DST gap.",
+  "enum": [
+    "reject",
+    "earlier",
+    "later",
+    "shift_forward"
+  ],
+  "examples": [
+    "reject"
+  ],
+  "type": "string"
+}

addedOutput schema / properties / result / properties / values / properties / applied_resolution_policy

Added value: +{
+  "description": "unique, earlier, later or shift_forward.",
+  "type": "string"
+}

addedOutput schema / properties / result / properties / values / properties / dataset_version

Added value: +{
+  "description": "Immutable Calcgrid time-zone evidence-package version.",
+  "type": "string"
+}

changedOutput schema / properties / result / properties / values / properties / from_abbreviation / description

Previous value: -"Short zone name from ICU (e.g. EDT); 'GMT+9:30' style when the zone has no common English abbreviation."New value: +"Short zone abbreviation from the pinned IANA data build (for example EDT)."

addedOutput schema / properties / result / properties / values / properties / source_candidate_utc_datetimes

Added value: +{
+  "description": "Every UTC instant that matches the source wall time; two values for a repeated time and none for a gap.",
+  "items": {
+    "type": "string"
+  },
+  "type": "array"
+}

addedOutput schema / properties / result / properties / values / properties / source_sha256

Added value: +{
+  "description": "SHA-256 of the official IANA tzdata release artifact.",
+  "type": "string"
+}

addedOutput schema / properties / result / properties / values / properties / source_time_status

Added value: +{
+  "description": "unique, ambiguous or nonexistent under the pinned transition table.",
+  "type": "string"
+}

addedOutput schema / properties / result / properties / values / properties / source_url

Added value: +{
+  "description": "Version-specific official IANA release URL.",
+  "type": "string"
+}

addedOutput schema / properties / result / properties / values / properties / tzdb_version

Added value: +{
+  "description": "Pinned IANA release used for this result.",
+  "type": "string"
+}

Changed15 schema fields changedSep 25, 2026

changedOutput schema / description

Previous value: -"Unified result envelope (see /docs/response-format.md)"New value: +"Deterministic calculation result with typed values, units, formula, sources and timestamp."

addedOutput schema / properties / next_actions / items
```
Added value: +{
+  "type": "object"
+}
```

addedOutput schema / properties / request / properties

Added value: +{
+  "calculator_id": {
+    "type": "string"
+  },
+  "inputs": {
+    "type": "object"
+  },
+  "tool": {
+    "type": "string"
+  }
+}

addedOutput schema / properties / result / properties / calculator_id
```
Added value: +{
+  "type": "string"
+}
```
addedOutput schema / properties / result / properties / calculator_name
```
Added value: +{
+  "type": "string"
+}
```

addedOutput schema / properties / result / properties / entity_type

Added value: +{
+  "const": "calculation",
+  "type": "string"
+}

addedOutput schema / properties / result / properties / status

Added value: +{
+  "const": "completed",
+  "type": "string"
+}

addedOutput schema / properties / result / properties / units / additionalProperties
```
Added value: +{
+  "type": "string"
+}
```

addedOutput schema / properties / result / properties / values / properties

Added value: +{
+  "converted_date": {
+    "description": "Calendar date in to_zone.",
+    "format": "date",
+    "type": "string"
+  },
+  "converted_datetime": {
+    "description": "ISO 8601 date-time in to_zone including its UTC offset.",
+    "type": "string"
+  },
+  "converted_time": {
+    "description": "Wall-clock time in to_zone (HH:MM).",
+    "type": "string"
+  },
+  "converted_weekday": {
+    "description": "Day of the week of converted_date.",
+    "type": "string"
+  },
+  "day_difference": {
+    "description": "converted_date minus date: −1, 0 or +1. Unit: days.",
+    "type": "integer",
+    "x-unit": "days"
+  },
+  "from_abbreviation": {
+    "description": "Short zone name from ICU (e.g. EDT); 'GMT+9:30' style when the zone has no common English abbreviation.",
+    "type": "string"
+  },
+  "from_utc_offset": {
+    "description": "UTC offset of from_zone at that instant (±HH:MM).",
+    "type": "string"
+  },
+  "time_difference_hours": {
+    "description": "to_zone offset minus from_zone offset at that instant; positive when to_zone is ahead. Unit: h.",
+    "type": "number",
+    "x-unit": "h"
+  },
+  "to_abbreviation": {
+    "description": "Short zone name of to_zone at that instant.",
+    "type": "string"
+  },
+  "to_utc_offset": {
+    "description": "UTC offset of to_zone at that instant (±HH:MM).",
+    "type": "string"
+  },
+  "utc_datetime": {
+    "description": "The same instant in UTC (ISO 8601).",
+    "type": "string"
+  }
+}

addedOutput schema / properties / result / required

Added value: +[
+  "entity_type",
+  "calculator_id",
+  "status",
+  "values",
+  "formula",
+  "summary"
+]

addedOutput schema / properties / sources / items
```
Added value: +{
+  "type": "object"
+}
```
addedOutput schema / properties / success / const
```
Added value: +true
```
addedOutput schema / properties / timestamp / format
```
Added value: +"date-time"
```
addedOutput schema / properties / version
```
Added value: +{
+  "type": "string"
+}
```

changedOutput schema / required

Previous value: -[
-  "success"
-]New value: +[
+  "success",
+  "request",
+  "result",
+  "timestamp"
+]

First observedSep 25, 2026

TDQS

A4.8/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond annotations (readOnlyHint, idempotentHint, destructiveHint all true/false appropriately), the description discloses pinned tzdb version (2026d), reporting of both offsets, UTC instant, date changes, source-time status, and candidate UTC instants for repeated hours. It also provides the exact formula and resolution policy handling, which adds significant behavioral context beyond what annotations convey.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is comprehensive but well-structured with clear sections (when to use, when not, what it computes, examples, inputs, outputs, formula, fallback). It front-loads the core usage instruction and uses bullet-like formatting for clarity. There is some redundancy (examples repeated in prose and JSON), but overall it is efficient and readable.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The description covers all necessary aspects: purpose, usage conditions, behavior, parameters (with examples), outputs (enumerated), the underlying formula, and even a direct REST fallback for verification. It is complete for an agent to invoke the tool correctly without needing additional context.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% with detailed descriptions for every parameter. The description adds value through complete JSON examples and clarifies the resolution_policy in the context of repeated hours (via behavioral description and formula). It doesn't repeat schema details but supplements with usage context, justifying a score above the baseline of 3.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description explicitly states the tool converts wall-clock date/time between IANA zones on a specific date, with a clear verb ('converts') and resource ('time between zones'). It distinguishes from siblings by naming alternatives (world-clock, unix-timestamp, time-duration) and instructs the agent to call the tool directly rather than computing manually.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides explicit when-to-use ('when you need to know what time an event scheduled in one city corresponds to in another') and when-not-to-use conditions with named alternatives ('Do not use this when you need the same instant in many zones at once (use world-clock)...'). Also instructs to call the tool directly and return its calculation, which is a clear directive.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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