Japan Postal Code Lookup MCP

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

No annotations are provided, so the description carries the full behavioral burden. It discloses that postcodes can span multiple towns, but omits auth/Pro requirements, read-only nature, output shape, rate limits, and error behavior.

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

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

The description is two short sentences with no filler, and the multi-town caveat is useful. The leading 'PRO.' is ambiguous, but overall the text is appropriately sized and front-loaded.

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

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

This is a two-parameter lookup with no annotations, no output schema, and only 50% schema coverage. The description explains result breadth but leaves auth requirements, return structure, and sibling selection unaddressed, so it is too thin for the tool's complexity.

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

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

Schema coverage is 50%: access_token is documented, but the required postcode parameter has no schema description. The description says 'for one postcode' but adds no format, syntax, or token semantics, so it fails to compensate for the undocumented required parameter.

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

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

States it returns all address matches for a single postcode and notes that some postcodes span multiple towns. This clearly identifies the resource and scope, but it does not name or distinguish postal_lookup or batch_postal, so sibling differentiation is missing.

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

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

There is no explicit when-to-use or when-not-to-use guidance. The only hint is 'all matches' and the multi-town caveat; it never directs agents to postal_lookup or batch_postal for alternative cases.

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

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

No annotations, so the description carries the full behavioral burden. It does disclose two real traits — a hard 50-item batch ceiling and, via "PRO.", a paid/subscriber gate — but says nothing about read-only semantics, partial-failure behavior for invalid postcodes, rate limits, or the shape of results.

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

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

Extremely compact and front-loaded, with the pro-tier marker first and the constraint second. Nothing is wasted, though the terseness borders on under-specification rather than deliberate concision.

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

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

For a tool with no annotations and no output schema, the description should explain at least what a resolution returns and how failures are surfaced. Neither is present, and the sibling relationship that would orient an agent is left entirely implicit.

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

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

Schema coverage is 50%: access_token is documented in-schema, while the postcodes array has only a type. The description partially compensates by supplying the critical max-size constraint (50) on that undocumented parameter, but adds nothing about format (7-digit? hyphenated? with/without 〒).

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

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

"Resolve up to 50 Japanese postcodes" gives a verb and a resource, plus a useful scope limit, but "resolve" is vague — it never says what a postcode resolves into (addresses? regions?). It also fails to differentiate from the sibling postal_lookup, which presumably does the same thing for one postcode.

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

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

No when-to-use guidance and no mention of the sibling tools. An agent cannot tell from this text why it should pick batch_postal over postal_lookup or all_matches, or what happens if the input exceeds 50 items.

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

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

No annotations exist, so the description carries the full burden. 'FREE' usefully signals no cost/auth barrier and the return fields are named, but nothing is said about invalid/unknown postcodes, accepted input formatting (hyphen or not), or error behavior for a lookup that can clearly fail.

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

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

Two short fragments, front-loaded cost note then the core action — nothing wasted. It is perhaps over-terse for the amount of input-format ambiguity the tool has.

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

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

For a one-parameter, no-annotation, no-output-schema lookup, naming the returned fields is the main thing needed and it is present. Missing input-format and failure-mode guidance leaves the definition adequate but not complete.

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

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

Schema coverage is 0% and the single string parameter is undocumented in the schema, but the description compensates partially by specifying the value must be a 7-digit Japanese postcode. It stops short of stating whether hyphens or spaces are tolerated, or whether leading zeros matter.

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

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

States a specific verb (Resolve) and resource (7-digit Japanese postcode), plus the shape of the result (prefecture/city/town). An agent can tell this is a single-postcode geocoder, though it never names the sibling batch_postal to contrast the single vs batch split.

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

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

Usage is only implied — the '7-digit' singular framing suggests one postcode at a time and siblings like batch_postal/all_matches hint at alternatives, but the description never says when to use this instead of them or what those tools do.

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