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

Beyond the readOnly/idempotent/non-destructive annotations, it discloses the default return contents (availability, centroid, bounding box), the effect of include_polygon, historical-first ordering, the no-automatic-successor-substitution rule, and the missing year-selection capability. These are exactly the non-obvious behaviors an agent cannot get from structured fields.

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 short sentences, front-loaded with the scope constraint and return behavior before caveats; nothing is filler. The line 'Obtain any descendant IDs before this call' is terse to the point of being cryptic, which costs a point.

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 read-only, batch-capable lookup with a full input schema and an output schema, the description covers scope, defaults, geometry opt-in, ordering, and known limitations. The only thin spot is how to obtain descendant IDs, which is a minor omission given the sibling catalog.

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 the schema already documents every parameter, including include_polygon and loc_ids. The description's mention of include_polygon=true adding GeoJSON coordinates largely restates the schema text, and batch_id/request_id tracing parameters get no added context, so it hovers at the baseline.

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?

The description gives a specific verb and resource ('Shape lookup') and constrains it to 'exact existing loc_ids only', which implicitly separates it from the resolve_* / identify_* siblings that handle unknown references. It does not name a sibling explicitly, so the differentiation is inferential rather than stated.

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?

It states a prerequisite ('Obtain any descendant IDs before this call'), a scope limit ('exact existing loc_ids only'), and an exclusion ('Year selection is not yet supported'). It stops short of naming the tool to use when IDs are unknown or how to obtain descendants, leaving one inference step.

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