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

Annotations already declare readOnly/idempotent/non-destructive, so the bar is lower; the description adds real context by disclosing the built-in density table (PLA, PETG, ABS, ASA, TPU, Nylon, PC, CF blends) and that leftover estimation works from gross spool weight. It does not explain what happens when both grams and meters are supplied, which is the one behavioral ambiguity.

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 tight sentences, capability list front-loaded and the invocation constraint placed last where it is easy to find. The material enumeration is long but load-bearing; nothing is redundant padding.

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 9-parameter tool at 44% schema coverage with no output schema, the description covers the main conversion/cost/spool use cases but leaves the spool-weight parameter interplay and the return shape unspecified. Adequate but with clear gaps an agent must resolve by trial.

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 44%, so the description must compensate, and it does clarify the grams/meters either-or that the schema leaves unstated (0 required params). However, the spool parameters (spool_weight_kg, empty_spool_weight_grams, spool_gross_weight_grams) and how cost is derived from spool_price_usd are never explained in prose.

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 concrete verbs and resources: grams→metres conversion, volume, cost, and remaining-on-spool estimation, with the material density set named. It is clearly distinct from calculate_layer_heights and calculate_volumetric_flow, though it never addresses overlap with the sibling calculate_print_cost, which also computes cost.

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 closing line 'Give either `grams` or `meters`' tells the agent how to invoke it, but there is no guidance on when to pick this tool over calculate_print_cost or the other calculate_* siblings, and no mention of which inputs are mutually exclusive versus combinable.

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