apod

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

With no annotations, the description carries the burden of explaining behavior. It discloses timezone-dependent availability, a 404 retry strategy, and the full return shape. It does not explicitly state read-only status or auth needs, but these are reasonable for a public NASA API.

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 concise and well-structured with Args and Returns sections. No waste; every sentence adds useful information about format, defaults, or output fields.

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 single-parameter read-only API with no output schema, the description covers the essential behavior, output fields, and a date edge case. It could be slightly richer on media_type semantics or error responses, but it is sufficient for successful invocation.

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?

The input schema has zero description coverage for the date parameter, and the description fully compensates by specifying format ('YYYY-MM-DD'), empty default, timezone nuance, and error recovery. This is exactly the needed parameter-level detail.

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 clearly identifies the resource as NASA's Astronomy Picture of the Day and lists the returned fields (title, explanation, image URL). It lacks an explicit verb like 'fetch' and does not explicitly distinguish from sibling tools, but the resource is unambiguous.

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?

Provides operational guidance for the date parameter (empty = today, US Eastern time, 404 fallback to yesterday) but does not state when to choose this tool over siblings like daily_art or sky_tonight. Usage is implied rather than explicit.

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