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

With no annotations, the description carries the full behavioral burden; it does disclose a real cost signal (x402, $0.01/call USDC eip155:8453) and that results are deterministic astronomy from NOAA equations. It stops short of stating coordinate conventions (decimal degrees?), whether atIso is truly optional, saturation behavior above the horizon, or error modes — meaningful gaps for a paid computation endpoint.

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?

Purpose and outputs are front-loaded in the first sentence, use cases in the second, with the pricing note last. The third sentence ('Use this when an agent needs to azimuth, altitude and cardinal direction') is grammatically broken and mostly duplicates sentence one, a small waste in an otherwise tight definition.

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?

There is no output schema, and the description compensates well by explicitly listing the returned fields (azimuth, elevation, cardinal direction, right ascension, declination) plus cost and provenance. For a simple 3-parameter geo tool this is close to sufficient; only coordinate conventions and units are left unstated.

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% (lat, lon, atIso all documented), so the schema does the parameter work and the baseline is 3. The description adds only the framing 'for any coordinates' and 'right now — or at any timestamp', which loosely implies atIso selects the instant but gives no format or sign conventions beyond the schema.

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 and resource with enumerable outputs (azimuth, elevation angle, cardinal direction, RA/dec) computed from NOAA solar equations, which is far more concrete than the title alone. However, it never names its closest sibling geo_time_sunrise_sunset, so the agent must infer the boundary between 'where the sun is' and 'when the sun rises/sets' on its own.

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?

Offers application contexts (shadow math, solar-panel orientation, photo planning) and one 'Use this when...' sentence, which implies usage but is largely a restatement of the purpose. There is no when-not guidance and no routing to alternatives such as geo_time_sunrise_sunset or live_weather, so an agent gets context but no decision rule.

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