Fetter MCP

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

No annotations are provided, so the description must carry the full disclosure burden. It establishes the read-only nature through 'Check' and specifies the input constraint (exact version), but omits safety confirmations, error behaviors (what if package/version not found?), data sources, or return value structure.

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 sentences that are tightly focused: the first states purpose, the second states the critical input constraint. No filler or redundant text. Every word earns its place in guiding tool selection and invocation.

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?

Given no output schema exists, the description should ideally specify the return format (presumably boolean or vulnerability details). While the function name 'is_vulnerable' and 'Check if...' phrasing imply a boolean response, explicit return documentation is missing. Adequate for the simple single-parameter input, but incomplete regarding output contract.

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?

With 100% schema description coverage, the schema already fully documents the parameter name, type, and format with examples. The description reinforces the 'exact version' requirement but adds no additional semantic detail about the parameter beyond what the schema provides, meeting the baseline expectation.

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 uses a specific verb ('Check') with a clear resource ('specific package version') and scope ('known vulnerabilities'). It effectively distinguishes from siblings: contrasted with 'most_recent_not_vulnerable' (which finds safe versions) by focusing on checking a specific version, and with 'lookup' by requiring exact version precision.

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 description provides clear usage constraints by stating 'Requires an exact version specifier,' which implicitly defines when NOT to use the tool (when only a package name is available). However, it stops short of explicitly naming sibling alternatives like 'use lookup to search for versions first if you don't have an exact specifier.'

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 burden. It discloses the core query behavior ( finding versions/vulnerabilities) but omits critical behavioral details: output format (list vs. object), data source (PyPI/npm/etc.), error handling for missing packages, or the constraint that exact version lookups ignore pagination limits (documented only in schema).

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?

Single sentence of 24 words with no redundant phrasing. Information is front-loaded with the verb. However, misses opportunity to structure guidance on enumeration vs. specific lookup that would help with sibling differentiation.

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?

Adequate for input-side documentation given robust schema coverage, but lacks description of return values since no output_schema exists. Does not hint at result structure, list pagination behavior, or the 'retain_passing' filtering implication mentioned in parameter descriptions.

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?

Input schema has 100% description coverage, establishing a baseline of 3. The description mirrors the schema's explanation that the 'name' parameter can include optional version specifiers but adds no additional semantic context (e.g., typical package naming conventions) beyond what the schema already provides.

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 specific action ('Look up') and target resource ('package'), including the dual capability to enumerate available versions and identify vulnerabilities. Distinguishes implicitly from siblings 'is_vulnerable' (likely boolean check) and 'most_recent_not_vulnerable' (likely single result) by mentioning 'which versions are available' (plural enumeration).

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?

Implies usage for version discovery and vulnerability scanning but lacks explicit 'when to use' guidance versus siblings. No mention of prerequisites (e.g., exact vs. fuzzy version lookups) or when to prefer the sibling tools instead.

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 full burden. It successfully discloses filtering behavior (no known vulnerabilities) and sorting logic (most recent first), but lacks information on error handling (what if no safe version exists?), whether this is read-only, or data source scope.

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?

Single sentence of 11 words with zero waste. Front-loaded with the action ('Find') and immediately clear about scope. Every word earns its place.

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 single-parameter lookup tool, the description adequately covers the core concept. However, without an output schema, it could have specified the return format or error cases (e.g., what happens if the package has no safe versions).

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?

Input schema has 100% description coverage with the 'name' parameter well-documented including examples. The description adds no additional parameter details beyond what the schema provides, warranting the baseline score.

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?

Description uses specific verb 'Find' with clear resource 'version of a package' and condition 'no known vulnerabilities'. The specific focus on 'most recent' and 'not vulnerable' effectively distinguishes it from siblings like 'is_vulnerable' (which likely checks specific versions) and 'lookup' (generic package query).

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 by the purpose (use when you need the latest secure version), but the description does not explicitly reference sibling tools or provide when-to-use/when-not-to-use guidance comparing this to 'is_vulnerable' or 'lookup'.

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