measure

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

With no annotations, the description carries the full burden and does so: it discloses return contents and ordering for probe mode, that gaps between crossings are directly room widths and wall thicknesses, recursive group scanning with innermost-group attribution, ambiguous-name refusal, and that all lengths are in metres.

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?

Front-loaded with the one-line purpose, then enumerated modes, then return semantics. Dense but every sentence carries operative information; the mode descriptions are necessarily long because they encode mutually exclusive calling conventions.

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?

Despite seven parameters, zero required fields, nested objects and no output schema, the description supplies the mode-to-parameter mapping and the return shape, which are exactly the gaps the structured fields leave. An agent can call it correctly without further inference.

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 71%, and the description adds meaning the schema cannot: it binds the three modes to specific parameter pairs, clarifies face_id_* are persistent_id values, and explains group scoping semantics and the ambiguity-refusal rule. It stops short of documenting 'at' key requirements beyond what the schema already states via its example.

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?

Opens with a specific verb and resource ('Measure distances') and immediately enumerates the three distinct modes with the exact parameter combination each requires. No sibling tool in the list performs measurement, so this is unambiguous against the surrounding CRUD/geometry verbs.

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 constraint 'provide exactly one' mode and the per-mode parameter recipes give clear selection guidance for an agent deciding how to call it. It stops short of stating exclusions or failure modes for a malformed call, so it is strong context rather than a complete when/when-not rubric.

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