geometry.area_triangle

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

Annotations already declare readOnly/idempotent/closed-world, so safety is covered; the description adds real behavioral context — exact computation at input precision and independence from the caller's Decimal context precision — which an agent could not infer from the 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?

Four dense sentences with the formula front-loaded, followed by semantics, precision behavior, and the pitfall warning; no filler or repetition of the schema.

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 two-parameter pure calculation with an output schema present, the description covers inputs, constraints, precision semantics, and common error — nothing an agent needs to call it correctly is missing.

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 0% (only bare titles), so the description carries the full burden and does: it defines base and height geometrically, imposes constraints (finite, non-negative, same units, Decimal string), and prevents the most likely input error with the slant-side warning.

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+resource (compute triangle area) and gives the exact formula (base*height)/2 in Decimal, immediately distinguishing it from geometry.area_rectangle/area_circle/area_polygon siblings.

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?

Clarifies what base and height must be (same units, finite non-negative Decimal, perpendicular height) and explicitly warns that using a slant side as height yields a wrong result. It lacks explicit when-to-use vs. an alternative formula (e.g., Heron), but the misuse exclusion is a strong usage signal.

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