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

Annotations already cover the safety profile (readOnly, idempotent, openWorld=false), yet the description adds real behavioral context: it warns there is 'no published typical figure' and only ranges are returned, lists what is excluded from pricing, and notes the inclusion of an unpriced checklist, reference cards, and dated sources. 'Pure arithmetic, no network or model' usefully reinforces openWorldHint=false. It stops short of describing the exact return shape in full.

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?

Information-dense and front-loaded with the core purpose and scope exclusions first. Sentences are long and packed (the enumeration of checklist/cards/sources is slightly opaque), but nothing is wasted.

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?

There is no output schema, so the description carries the burden of explaining returns — and it does, covering the range-based output, the absence of a typical figure, the residential add-on band, and the supplementary material. For a read-only arithmetic calculator with full schema coverage, 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 description coverage is 100%, so the width/length semantics are already handled (baseline 3). The description adds meaning beyond the schema by explaining that use=residential 'adds the separate living-space build-out band with an open top and a combined planning estimate,' which the enum description only hints at.

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 ('Estimate pole barn construction costs') plus the scope ('for given dimensions, optionally finished as living space'), which cleanly separates it from the other cost calculators in the sibling list (driveway_cost, fence_cost, concrete_calculator). An agent can identify the tool without opening the schema.

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?

Gives clear scope boundaries for when this tool applies versus what it explicitly will not cover: 'Site work/slab/doors/height/permits are not priced' and 'building only.' However, it never names an alternative tool for those excluded items, so routing to a sibling is left implicit.

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