japanlaw.org — Japanese law

See what changes across the laws

list_changes

Read-onlyIdempotent

What changes in Japanese law between two days, across every law japanlaw.org holds — 来年施行される改正、4月1日に変わる法令 — or one law's, or one topic's. Each change: the day it takes effect (day: on that day; by, a day a Cabinet Order sets, that day at the latest; open, not set yet), whether it is still to come, the law, the amending Act (titles, law number), its version, and its url. With no until, every change still to come is listed, those with no day yet last; since defaults to today. A long list stops at limit; continued.cursor, passed back as cursor with the same arguments, goes on. For what one change does, provision by provision, call get_amendments with its law and version. Link each change by its url.

Input Schema

Name	Required	Description
`law`	No	One law's changes only: its Japanese title (労働基準法), English title, short name (労基法), slug or e-Gov law ID. Unset: every law's.
`lang`	No	The language of the pages every url opens, and of the card get_provision is drawn as: "en" (default) or "ja". The text returned always holds both languages.
`limit`	No	Changes per answer, 1–200; default 50.
`since`	No	The first day, YYYY-MM-DD (2027-04-01). Unset: today.
`topic`	No	Only the changes of one topic's laws: work, immigration, tax, social-security, business, consumers, civil, housing, crime, transport or government.
`until`	No	The last day, YYYY-MM-DD. Unset: every change still to come, however far off, and those whose day is not set yet.
`cursor`	No	Go on from here: the cursor an earlier answer's continued gave, with the same since, until, law and topic.

Output Schema

Name	Required	Description	Default
`since`	Yes
`today`	Yes
`total`	Yes
`changes`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

AddedNov 1, 2026

TDQS

A4.6/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent, non-destructive, non-open-world. The description goes beyond that by explaining the meaning of the day values (on/by/open), ordering ('those with no day yet last'), and pagination behavior. It does not discuss auth, rate limits, or error conditions, so it is not exhaustive, but it adds meaningful behavioral context.

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?

Front-loaded with the purpose in the first sentence. Dense but mostly earns its place; the Japanese snippets add some visual bulk without much functional value to an agent, and the parenthetical about day values is a bit compact, but overall it is efficient.

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?

Given an output schema exists, the description need not explain return values, and it still covers defaults, ordering, pagination, and routing to get_amendments. An agent has everything needed to call it correctly.

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%, so baseline is 3. The description adds interpretation beyond the schema: the semantic difference between 'since' and 'until' defaults, the meaning of the day statuses, and the requirement that cursor be reused with the same since/until/law/topic arguments.

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 — what changes in Japanese law between two days — with scope options (every law, one law, one topic). It also explicitly names the sibling get_amendments and what it is for, so an agent can distinguish the two without opening either schema.

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 covers defaults ('since defaults to today'), the no-until behavior, pagination instructions ('continued.cursor, passed back as cursor with the same arguments'), and the alternative for per-provision detail ('call get_amendments'). The when-to-use vs when-not-to-use is fully specified.

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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