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

Annotations only establish that this is a safe, non-destructive read; the description goes well beyond them by disclosing the return shape (fits ranked best-first, plain-word reasons, ruled-out materials and why) and two real behavioral limits: it does not rank by strength/stiffness, and safety-critical parts are escalated to a human. That escalation behavior is exactly the kind of thing an agent could not infer from schema or annotations.

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?

Three sentences, front-loaded with the usage trigger, then the return contract, then the boundaries. Every sentence adds information an agent needs and none is redundant with structured fields.

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 an output schema present the description need not explain return values, yet it still summarizes the ranked/reasons/ruled-out shape and the human-escalation rule. Combined with the annotations and fully documented enums, an agent has everything needed to call and interpret this tool; the only unmentioned detail is that all parameters are optional, which is evident from the schema.

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% with all seven enums documented, including defaults, so the schema carries the parameter burden and a 3 baseline applies. The description restates the criteria categories but adds no format, precedence, or interaction guidance (e.g., how conflicting criteria are resolved) beyond the 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?

States a specific verb and resource ('recommend which of our plastics suits a part') and immediately scopes it to selection-by-requirements, which separates it from list_materials. The description also names the ordering and the rationale output, so an agent knows exactly what kind of answer to expect.

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 opening 'Use this when someone wants help choosing which of our plastics suits a part' gives clear trigger conditions, and the enumerated criteria (indoor/outdoor, heat, impact, flexing, chemicals, looks, cost) tell the agent what inputs matter. It does not name an alternative sibling (e.g., list_materials for a plain catalogue) or state exclusions as routing advice, so it stops short of a 5.

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