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

Annotations already establish a safe, idempotent, closed-world read, so the bar is lower; the description still adds two useful pieces of context: the 20-credit Tier 2 cost and the warning that rising/setting curves arrive as several disjoint segments that are all returned. What it does not cover is latency, result size, or whether an invalid planet/angle pair is rejected.

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?

The core sentence is front-loaded and dense with signal, and the output-shape clause about disjoint segments earns its place. The bracketed Group/Cost tags are a house convention rather than prose waste, though they do dilute the front-loading slightly.

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 no explanation, yet the description still characterizes the payload shape usefully. For a 3-parameter, single-line report tool it is nearly complete; the missing piece is routing context against the many geo_acg siblings.

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% and the nested birth-data object is heavily documented in the schema itself, so the schema does the heavy lifting. The description's phrase 'planet-and-angle pair' gestures at the two selector parameters but adds no syntax, accepted values, or defaults beyond what the schema already states. Baseline 3 applies.

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 the specific resource (a single A*C*G line) and enumerates exactly what comes back: geometry, life areas with weight and polarity, and the interpretation text for the planet-and-angle pair. It is clearly narrower in scope than sibling astroway_geo_acg, but it never names that sibling or states the relationship explicitly, so the differentiation is left to inference.

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?

There is no when-to-use guidance at all. Nothing tells the agent to pick this over astroway_geo_acg (the full map), astroway_geo_acg_by_category, or astroway_geo_acg_best_places, nor what precondition (e.g. a previously identified line) should trigger a call.

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