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

Annotations already declare read-only/idempotent, but the description goes well beyond them: 10-minute caching, 503 upstream_unavailable on outage and that it is not charged, sub-second cached vs seconds-on-refresh latency, and the dark/clear-sky assumption where cloud, moonlight and light pollution are unmodelled. That is exactly the kind of behavioral context structured fields cannot convey.

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?

A single dense, front-loaded paragraph that leads with the meaning of the returned value before logistics. It is somewhat long and repeats the lat/lon ranges already in the schema, but every remaining sentence (cost, cache, outage) earns its place for an agent deciding whether to call it.

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 contract itself (chance 0-100 plus Kp, solar altitude, dark-enough flag), and also covers the cost, free-tier limit, caching and error mode. An agent has everything needed to decide to call it and interpret the result.

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% and both parameters carry their own range descriptions, so the schema does the heavy lifting. The description only restates the lat/lon ranges and frames them as a 'point', adding no real meaning beyond the schema. 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?

States a specific verb+resource: the percent chance of visible aurora overhead at a point, sourced from NOAA SWPC's OVATION model with a 30-90 minute horizon. This is clearly distinguishable from the sibling get_space_weather, which is a general space-weather lookup.

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 sets context (point-based, 30-90 min forecast, dark-sky assumption) but never states when to prefer this over the sibling get_space_weather or any alternative. Usage is implied rather than explicit, with no when-not guidance.

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