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

Annotations already declare readOnly, idempotent, non-destructive and non-open-world, so the safety profile is covered. The description adds useful behavioral context — results are date-ordered, dates are UK-local, and the visibility filtering determines whether eclipses seen only abroad appear — but since an output schema exists, the detailed field enumeration is partly redundant rather than purely additive.

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?

Two sentences, front-loaded with the core capability, and no filler. The second sentence is slightly dense and stacks several output characteristics, but every clause carries real information about what is returned.

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?

All five parameters are optional, schema coverage is complete, annotations are rich and an output schema exists, so the description only needs to frame scope and results — which it does. The one gap is behavior when no eclipses match the filter (empty result vs. earliest match), which an agent might want to know.

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%, so every parameter is already documented, including the 'from' default and the visibleFromUk semantics; baseline is 3. The description contributes only the extra detail that a place yields start/maximum/end times and coverage or Moon altitude per eclipse, which sharpens but does not transform the meaning of the 'place' parameter.

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 ('Returns upcoming solar and lunar eclipses') plus the scope ('from the UK', date order) and enumerates the payload: peak time, eclipse kind, London contact times, coverage/totality. That framing is clearly distinguishable from the sibling moon-calendar and moon-event tools, so no schema reading is needed to identify it.

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?

Usage is only implied: the description makes clear this is for looking up upcoming eclipses visible from the UK, and the second sentence hints that supplying a place enriches the result. There is no explicit guidance on when to prefer a sibling tool (find_moon_events, get_moon_calendar) for related sky events, and no mention of when the list would be empty.

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