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

Annotations already declare readOnlyHint=true, openWorldHint=true, and destructiveHint=false. The description adds valuable behavioral context beyond annotations: bundled ids resolve offline, non-bundled ids require partsBaseUrl, and the return value includes cache path and sha256 fingerprint. This explains the caching mechanism and external dependency, which annotations alone do not capture.

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 concise (four sentences) and front-loaded with the primary use case. Every sentence adds value: when to use, resolution logic, offline vs online behavior, and return format. No redundant or wasteful text.

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?

The description provides enough information to use the tool for its main purpose, covering id/query resolution, bundled vs non-bundled, and return values. However, it leaves gaps: the roles of 'family', 'category', and 'standard' are unexplained, and it does not clarify whether id and query can both be provided or their interaction. Given the low schema coverage and 6 parameters, the description is adequate but not fully 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 description coverage is only 17% (only partsBaseUrl has a description). The description explains the roles of 'id' and 'query' (resolve an id or single-match query), but does not address 'family', 'category', or 'standard' parameters. These remain ambiguous—whether they are part of the query or separate filters is unclear. With low coverage, the description should have compensated by detailing all parameters, but it only covers two out of six.

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 clearly states the tool's purpose: to download a catalog part as a STEP file. It specifies the action (download/fetch) and the resource (catalog part STEP file), and distinguishes from siblings like find_part (search) and add_part (adding parts) by focusing on file download. The verb 'fetch' combined with 'download a catalog part as a STEP file' is 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.

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

The description provides clear context on when to use the tool: 'Use this when you need to download a catalog part as a STEP file.' It also explains the resolution mechanism (id vs single-match query) and the difference between bundled and non-bundled ids with partsBaseUrl. However, it does not explicitly exclude alternative tools (e.g., find_part for searching or add_part for placement) or provide when-not-to-use guidance, which would improve clarity.

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