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

Annotations already establish read-only, idempotent, non-destructive behavior. The description adds valuable operational context beyond that: no auth required, free commercial use, timezone auto-detection, and the breadth of returned sun/moon fields. It doesn't mention rate limits or error behavior, but annotations lower the burden here.

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 description is one dense, well-organized paragraph with a front-loaded verb and resource, a useful return-field list, then input options and auth/commercial notes. Every sentence earns its place; there is no filler.

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?

For a simple read-only single-day astronomy query with a full output schema, the description covers the input contract, supported dates, timezone handling, time format options, return fields, and auth/commercial terms. Nothing needed to invoke it correctly is missing.

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 description mostly restates what the schema already says: accepted date formats, IANA timezone names, and 12h/24h/Unix time formats. It adds little new meaning beyond the structured parameter definitions.

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 first sentence names a specific verb and resource: "Get complete daily astronomical data for any lat/lng and date from SunriseSunset.io." The long field list (sunrise, sunset, dawn, moonrise, moonset, etc.) clearly distinguishes it from narrower siblings like sunrisesunset.moon.phase and sunrisesunset.sun.position.

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 makes the intended use clear: single-day daily astronomical data for arbitrary coordinates and dates, with date, timezone, and time-format options specified. It does not explicitly name alternatives or say when not to use this tool, so it falls short of a 5.

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