Quantity roll-up

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

Annotations already cover the safety profile (readOnlyHint, openWorldHint=false), and the description adds genuinely non-obvious behavior: unit normalization to m/m2/m3 and, crucially, that each group reports `without_quantity` alongside `count` so incomplete totals are self-evident. It does not say what happens when the named quantity is absent everywhere or on error, keeping it below 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?

Opens with the operation and grouping before any caveat, which is the right ordering. The second paragraph's aphorism about 40 of 200 walls is slightly editorial but does justify the `without_quantity` field, so it mostly earns its space.

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 no output schema, the description carries the return-value burden and does so for the main fields (group key, count, without_quantity). It stops short of describing the shape of group labels or behavior on unknown quantity names, but an agent has enough to call it correctly.

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 every parameter is already documented in the schema, and the description adds only the example quantity names and the unit-conversion note. Baseline 3 is appropriate since the schema does the heavy lifting.

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 ('Total a named quantity ... over a selection') plus the grouping axis, which is more precise than any sibling like bim_model_summary or bim_property_values. An agent can tell this is the aggregation tool versus the listing/detail tools 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?

The description implies when to use it (you want a rolled-up total rather than per-element values) and names the grouping options, but never states exclusions or points to an alternative such as bim_property_values for distinct values or bim_elements_by_type for per-element listings. Usage is inferable rather than directed.

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