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

Goes well beyond the readOnly/idempotent annotations by disclosing data freshness (precomputed every few hours by Vigi-Sky), the degraded-precision path for lat/lon, and the side artifact produced (calendar feed with a 10-minute alarm). Missing only a note on latency/staleness bounds for the precomputed passes, which keeps it from a 5.

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?

Three sentences, each carrying distinct load: capability, routing rule, and data provenance. The A-to-B contrast with iss_passes is placed early where it matters most for routing.

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?

Output schema exists, so return values need no explanation; annotations cover the safety profile. With zero required parameters, the remaining risk — the agent assuming worldwide coverage or fresh computation — is exactly what the description preempts.

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 baseline is 3; the description earns above that by adding meaning the schema cannot express — that lat/lon is a fallback snapping to the nearest covered city, and that city must be one of a bounded, enumerated set. It does not mention the lang parameter, but the schema already handles it.

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 ('Give the next naked-eye passes of the ISS (and Tiangong)') plus a precise scope (41 cities across five countries). It explicitly contrasts itself with the sibling iss_passes, so an agent can route without opening either schema.

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?

Gives explicit selection criteria: use when the user names a city or wants an alert; use iss_passes for other coordinates. It also covers the in-between case (arbitrary lat/lon snaps to the nearest covered city), eliminating the main ambiguity an agent would face.

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