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

With no annotations the description carries the full burden, and it does disclose the crucial behavioral trait: the check is purely local and syntactic, so it cannot confirm the number actually exists or is registrable. It does not describe the response shape or behavior on malformed input, which keeps it out of 5 territory.

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?

Very short and front-loaded with the key constraint (zero network, zero cost). The bilingual restatement duplicates content, which is defensible for i18n but means every claim appears twice.

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 simple three-parameter check the description covers the essential scope, but with no annotations and no output schema it says nothing about return values or how errors are surfaced — notable given the sibling get_error_codes implies a structured error surface the agent should know about.

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 description coverage is 100%, so all three parameters (vat, vatNumber, countryCode) are already documented in the schema, including the prefix/no-prefix distinction. The description adds nothing about how these fields interact (e.g. whether countryCode is required when vat includes a prefix), so the baseline 3 applies.

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 and resource (VAT number format validation) and pins down the scope with "format-only" and "纯本地". The contrast with the sibling validate_vat is inferable from "format-only / 零网络", but the sibling is never named, so it stops short of a full 5.

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 implied rather than stated: "zero network, zero cost, format-only" suggests a cheap syntactic pre-check, but the description never says when to prefer this over validate_vat or when it is insufficient. No exclusions or prerequisites are given.

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 are provided, so the description carries the full burden. It discloses that the return is a complete (not filtered) bilingual table, which implies a safe, read-only, no-argument lookup, but says nothing about size, format, auth requirements, or rate limits.

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 sentences, front-loaded, with no wasted preamble. The bilingual restatement is slightly redundant but appropriate for a bilingual product surface.

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?

With no output schema, the description must convey return content, and it does state that a full bilingual error-code table is returned. It stops short of describing the table's fields or how codes map to messages, but for a trivial zero-argument lookup this is largely sufficient.

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?

The tool takes zero parameters, so the baseline of 4 applies. The description adds nothing about parameters because there are none to describe.

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 and resource: it returns the full VAT validation error-code table, and adds the bilingual (Chinese/English) scope. This is clearly distinguishable from siblings like validate_vat and check_vat_format, though it never explicitly contrasts itself with them.

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 when-to-use guidance, no prerequisites, and no mention of alternatives. The agent must infer from the name alone that this is a reference lookup to call when interpreting error codes returned by validate_vat.

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 are provided, so the description carries the full burden, and it does disclose the shape of what comes back (country code plus three naming variants). It does not say whether the list is static, cached, or sourced live from VIES, which is the one behavioral fact that would matter for a reference-data tool.

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 sentences with the resource front-loaded and concrete examples (USt-IdNr., Partita IVA, btw-nummer) that make the output tangible. The English sentence is largely a restatement of the Chinese one, which is mild redundancy but appropriate for a bilingual audience.

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?

With no output schema, annotations, or parameters, the description is the sole carrier of information, and it does describe the returned fields. Nothing an agent needs in order to invoke this trivial zero-arg tool is missing, though origin/freshness of the list is unstated.

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?

The tool takes zero parameters, so the baseline of 4 applies. There is nothing for the description to clarify beyond the empty schema.

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?

The description states a specific verb and resource ('return the list of countries that support VAT validation') and enumerates the returned fields (code, native name, local VAT term, Chinese/English names). It does not explicitly distinguish itself from siblings like validate_vat, but the noun phrase 'list of countries' makes the scope unmistakable.

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: an agent would infer this is a reference lookup to run before or alongside validate_vat/check_vat_format. There is no explicit when-to-use statement, no mention of the sibling tools, and no guidance on whether this list should gate validation calls.

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?

With no annotations provided, the description carries the full behavioral burden. It usefully discloses that the live VIES step is an external EU-official call performed only after the free local check passes, signaling latency/cost, but it omits rate limits, auth requirements, error behavior, and return format — all relevant for a network-backed validation tool.

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 front-loaded sentences that lead with the action name, with the enrichment (local then live) stated first. The bilingual duplication roughly doubles length but the content is efficient and there is no filler.

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?

With no output schema and no annotations, the description must carry more, yet it stops at the two-stage flow. It does not describe what a validation result looks like, how errors surface (despite a get_error_codes sibling existing), or how cache and VIES affect the outcome, leaving real gaps for a 5-param external-API tool.

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 description coverage is 100%, so the schema already documents vat, live, useCache, vatNumber, and countryCode. The description adds no format/syntax detail beyond what the schema provides, so baseline 3 applies.

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 (validate) and resource (VAT / tax ID number), and describes a concrete two-stage behavior: free local format check followed by optional live VIES verification. It implicitly distinguishes itself from the format-only sibling by mentioning the live verification step, but never names check_vat_format, so the sibling boundary is left for the agent to infer.

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?

The staged description ('先做免费本地格式校验，再按需调用 VIES') implies when the live call fires versus when the cheap local check is enough, which indirectly guides the `live` flag. However, it never explicitly states when to prefer this tool over check_vat_format or when not to use it, leaving the alternative routing unstated.

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