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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety and determinism are covered structurally. The description adds the cost tier (50 credits, Tier 3), which is genuinely useful behavioral context not present in annotations, and describes the output as lines plus angular distance, but adds nothing on limits or radius semantics.

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?

Two front-loaded sentences: purpose first, then a memorable use-case tag, followed by compact group/cost metadata. No sentence is wasted and nothing is buried.

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?

An output schema exists, so return values need not be explained, and the annotations plus a fully documented input schema carry most of the burden. What remains thin is the operational context around what counts as a line and how the radius filters results, but for a single-purpose geo lookup this is close to sufficient.

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%, with detailed inline documentation for body, fields and precision, so the baseline is 3. The description alludes to radiusDeg by name ('within radiusDeg') but adds no meaning beyond what the schema's min/max/default already convey.

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 names a concrete resource and scope: 'A*C*G lines passing within radiusDeg of one location, with the angular distance to each', which is a specific verb+resource rather than a restatement of the title. It stops short of distinguishing itself from the many geo_acg siblings (astroway_geo_acg, astroway_geo_acg_line_report, astroway_geo_acg_by_category), so an agent must infer the boundary itself.

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 "what runs over this city" lookup' gives a clear situational framing for when the tool applies. However, it offers no when-not condition and never names an alternative sibling (e.g. the broader line report) that would be preferred for a different question, leaving the routing decision implicit.

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