Calcgrid

IANA Time Zone Transition List

list_time_zone_transitions

Read-onlyIdempotent

Use this when you need the next or historical daylight-saving/offset changes for scheduling, payroll, travel, audits or a regression test, with a specific reproducible tzdb version. 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 only need to convert one ordinary date-time, need legal advice about a jurisdiction's time law, or need changes announced after this pinned release. What it computes: Lists every UTC-offset transition for one IANA zone and date range using pinned tzdb 2026d, including the local boundaries, offsets, abbreviations and whether the clock creates a gap or overlap. Example user requests: List every 2026 UTC-offset transition in America/New_York with local boundaries. | When does Australia/Adelaide change clocks between 2026-01-01 and 2027-01-01? | 列出 Europe/London 在 2026 年的夏令时转换点、前后偏移和 IANA 数据版本。 Inputs: time_zone (string); start_date (date); end_date (date). Complete JSON argument examples: {"time_zone":"America/New_York","start_date":"2026-01-01","end_date":"2026-12-31"} Outputs: time_zone, resolved_zone_id, start_date, end_date, transition_count, transitions, tzdb_version, dataset_version, source_url, source_sha256, coverage_note. Formula: select zone transition instants whose local boundary before or after lies inside [start_date, end_date] Direct REST fallback: POST https://tttkmbb.com/api/v1/calculate/time-zone-transitions with the same JSON input fields. Do not guess another /api/* path. Docs: https://tttkmbb.com/time/time-zone-transitions.md

Input Schema

TableJSON Schema

Name	Required	Description
`end_date`	Yes	Last local calendar date to inspect; ranges may not exceed 3,660 days.
`time_zone`	Yes	IANA zone identifier present in tzdb 2026d.
`start_date`	Yes	First local calendar date to inspect (1900-01-01 through 2100-12-31).

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: +[
+  {
+    "end_date": "2026-12-31",
+    "start_date": "2026-01-01",
+    "time_zone": "America/New_York"
+  }
+]

AddedSep 26, 2026

TDQS

A4.7/5.0

Behavior5/5

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

Annotations already mark the tool as read-only, idempotent, and non-destructive. The description adds meaningful behavioral context: pinned tzdb 2026d, inclusion of gap/overlap flags, the precise selection formula, and a direct REST fallback path. No contradiction with annotations.

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

Conciseness5/5

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

The description is long but well-structured with clear sections: use cases, exclusions, computation details, examples, inputs, outputs, formula, fallback, and docs. It is front-loaded with the most important decision information and every section earns its place.

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?

For a 3-parameter tool with an output schema and read-only annotations, the description is complete. It covers invocation scenarios, exclusions, a complete JSON example, the calculation formula, expected outputs, and a fallback endpoint. Nothing needed to call the tool correctly is missing.

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

Parameters3/5

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

Schema coverage is 100%, with each parameter already having type, format, examples, and constraints. The description restates the inputs and clarifies date-range inclusion via the formula, but it does not add substantial new parameter-level meaning beyond the schema.

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?

States a specific verb and resource: 'Lists every UTC-offset transition for one IANA zone and date range using pinned tzdb 2026d.' It also distinguishes itself from ordinary date-time conversion and from tools that need post-pinned-release changes.

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?

Explicitly says when to use it (scheduling, payroll, travel, audits, regression tests with reproducible tzdb) and when not to use it (single date-time conversion, legal advice, post-pinned-release changes). Also instructs the agent to call the tool directly and return its calculation rather than answering from memory.

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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