Server Quality Checklist

Tool Scores

• list_supported_countriesA
  3.6/5.0
  Behavior2/5

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

  With no annotations, the description must disclose behavioral traits. It states the tool distinguishes EU from non-EU countries, which is helpful, but it does not clarify the output format (e.g., names, codes) or whether non-European countries are included. Missing details like response structure or potential limitations.

  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 two concise sentences, front-loading the core purpose and adding a key distinction. Every sentence adds value without redundancy.

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

  Completeness2/5

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

  No output schema is provided, so the description must explain return values. It mentions a list of countries with a distinction between EU and non-EU, but it does not specify the exact format (e.g., ISO codes, names), whether non-European countries are included, or the structure of the response. This leaves ambiguity.

  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?

  The tool has no parameters and 100% schema coverage. The description does not need to add parameter info, so baseline score of 4 is appropriate.

  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 clearly states that the tool returns a list of countries with VAT data from the vatnode MCP server, and it distinguishes between EU member states and other European jurisdictions. This is specific and differentiates the tool from siblings like list_eu_vat_rates.

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

  Usage Guidelines3/5

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

  The description implies usage when you need to know supported countries, but it does not explicitly state when to use this tool over siblings like get_country_vat_rates or check_vat_format. No when-not or alternative guidance is provided.

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

• check_vat_formatA
  4.4/5.0
  Behavior4/5

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

  With no annotations provided, the description carries the full burden. It discloses that the check is offline, syntactic only, does not verify with VIES, and is free with no API key required. However, it does not describe the return format (e.g., boolean or error), which would enhance transparency further.

  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 two sentences, with the first sentence stating the core purpose, the second adding limitations and usage context. Every sentence is valuable, and the structure is front-loaded.

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

  Completeness4/5

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

  Given the tool has one parameter, no output schema, and no annotations, the description covers purpose, usage, and key behavioral traits well. It is missing explicit mention of the response, but for a simple check tool this is acceptable.

  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%, so the schema already documents the parameter well. The description does not add extra meaning beyond what is in the schema's parameter description. Baseline 3 is appropriate.

  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 clearly states it performs an offline syntactic check of a VAT number against country-specific regex patterns, and explicitly distinguishes from the sibling tool validate_vat_number. The verb 'check' and resource 'VAT format' are specific and unambiguous.

  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?

  The description explicitly says when to use (quick sanity check, free, no API key) and when not to use (if VIES verification is needed, use validate_vat_number). It provides clear context and an alternative tool.

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

• get_country_vat_ratesA
  4.4/5.0
  Behavior4/5

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

  With no annotations, the description carries the full burden. It discloses the tool is free and requires no API key, implying a read-only operation. It details the output content. It does not mention error handling or rate limits, but the level of detail is adequate for a simple tool.

  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?

  Three well-structured sentences. The first sentence lists what is returned, the second explains input format and coverage, and the third states usage trigger and free nature. No redundancy.

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

  Completeness4/5

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

  Given a simple tool with one parameter and no output schema, the description covers usage, input semantics, output content, and a behavioral note. Missing error handling or details on response format, but overall complete for typical agent invocation.

  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 a clear description of the parameter. The tool description adds context by specifying the set of valid countries (European jurisdictions) and the format expectations, going 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?

  The description clearly states the tool returns standard, reduced, super-reduced, and parking VAT rates along with VAT number format and regex for a single European country. It specifies the input format (ISO 3166-1 alpha-2). It distinguishes from sibling tools by focusing on a single country's full rate set, unlike list_eu_vat_rates which likely lists all countries, or check_vat_format which checks format validity.

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

  Usage Guidelines4/5

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

  Explicitly says 'Use when the user asks "what is the VAT rate in X" or needs the VAT number format for a country.' It also notes coverage of non-EU European jurisdictions. While it doesn't explicitly list when not to use or alternatives, the guidance is sufficient for common use cases.

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

• list_eu_vat_ratesA
  4.6/5.0
  Behavior4/5

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

  No annotations provided, so description carries full burden. It discloses data source (EU Commission TEDB), update frequency (daily), and that it's free with no API key required. However, it could explicitly state it's read-only and has no side effects.

  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?

  Three sentences: first states purpose, second provides usage guidance, third adds data source and constraints. No wasted words, front-loaded with most important information.

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

  Completeness4/5

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

  Given simple tool with no parameters and no output schema, description is nearly complete. It covers purpose, usage, source, update frequency, and cost. Minor gap: does not describe return format (e.g., map of country to rates), but output schema is absent so that expectation is low.

  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?

  Zero parameters, so description need not add parameter meaning. Schema coverage is 100% (empty). Baseline for 0 parameters is 4, and description correctly focuses on tool behavior without parameter clutter.

  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?

  Clearly states it returns current VAT rates for all EU member states plus Northern Ireland. Distinguishes from sibling get_country_vat_rates by noting preference for single country queries.

  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 tells when to use (overview, comparison, 'all EU VAT rates') and when not to (single country, prefer get_country_vat_rates). Provides clear guidance on alternatives.

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

• validate_vat_numberA
  5/5.0
  Behavior5/5

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

  Discloses that it connects to VIES, returns metadata, and optionally provides a consultation number for audit trails. No destructive behavior; API key requirement and country limitations are stated.

  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?

  Concise paragraph with clear flow: main purpose, special case, when to use, prerequisites and limitations. No redundant sentences.

  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?

  Fully describes output (validity, company info, registration date, consultation number) and constraints (EU-27+XI, API key). No output schema, so description carries complete burden.

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

  Parameters5/5

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

  Adds meaning beyond schema: explains requesterCountryCode/requesterVatNumber pair yields consultation number, and that vatId has spaces/dashes stripped. Schema coverage is 100% but description enriches it.

  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 clearly states the tool verifies EU VAT numbers against VIES, listing specific returned data. It is distinct from siblings like check_vat_format (format only) and others (rates/lists).

  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 states use cases: confirm VAT real, look up company, evidence for compliance. Also mentions API key requirement and supported countries, providing clear context for when to use.

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