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

Annotations already declare readOnlyHint, destructiveHint=false and openWorldHint=false, and the description adds real behavioral guarantees beyond that: it will not fabricate costs and it reports which number is missing. That missing-value disclosure is the kind of failure-mode behavior annotations cannot express. The rest ('returns the totals for each, the crossover quantity...') largely restates what the output schema already conveys, which keeps it from a 5.

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 when-to-use clause, then outputs, then the reliability caveat. No filler and no repetition of the tool name or title.

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 seven optional parameters (zero required), a full output schema and clear annotations, the description covers purpose, inputs, outputs and trust behavior adequately. The one gap is that it never explains what happens if the user supplies no numbers at all, which matters given that every parameter is optional.

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 coverage is 100%, so the schema already documents all seven parameters with units, defaults and bounds, making 3 the baseline. The description adds little parameter meaning and only names four of the seven inputs (quantity, printed unit cost, tooling cost, molded unit cost), silently omitting setup_cost, revision_cost and tool_revisions, which could mislead an agent into ignoring revision-related costs.

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 (compare) and two specific resources (3D printing vs injection molding) plus the scope (for a quantity, using the user's own numbers). This is clearly distinguishable from siblings like get_print_quote or recommend_material, which do different jobs.

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?

'Use this when someone wants to compare 3D printing with injection molding for a quantity, using their own numbers' gives a clear triggering condition and even constrains the input mode (user-supplied figures, not a quote lookup). It does not name an alternative tool or state when not to use it, 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.