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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds real value beyond that by disclosing that results come from a saros/draconic-cycle approximation and that dates and kinds are indicative — a caveat an agent needs in order to present output with appropriate hedging.

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?

A single sentence with the prediction scope front-loaded and the approximation caveat tucked into a parenthetical. Nothing repeats the title and nothing could be cut without losing meaning.

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 two-optional-parameter read-only tool with full schema coverage and annotations, the description covers purpose, scope and reliability. The only soft gap is the return shape: 'dates & kinds' hints at the payload, but there is no output schema, so the agent learns the field structure only at call time.

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%, with both 'days' (range 1-1825, default 365) and 'tanggal' (YYYY-MM-DD, default today) fully documented in the schema. The description only restates the horizon concept, adding no format or interaction detail beyond what the schema already supplies, so the baseline 3 applies.

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 gives a specific verb ('Predict') and resource ('upcoming solar & lunar eclipses') plus a scope qualifier ('within a given horizon of days'), which clearly separates it from the nearby astronomi_sun, astronomi_moon and astronomi_twilight tools. It stops short of naming those siblings explicitly, so differentiation is by resource rather than routing guidance.

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?

Use is implied by the horizon-of-days framing, but there is no explicit statement of when to reach for this tool versus astronomi_moon / astronomi_moon_next, nor any prerequisite or exclusion. An agent can infer the use case but must reason about alternatives on its own.

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