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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile needs no restating. The description adds genuine value by naming the return fields (phase name in both Indonesian and English, lunar distance), but says nothing about the output shape, precision, or range limits of the date.

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 front-loaded sentence with the resource first and the returned fields after the colon; no filler or hedging. Every clause carries information.

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 one-optional-parameter read tool with strong annotations, the definition is nearly sufficient, and listing output fields compensates for the absent output schema. The remaining gap is the lack of differentiation from astronomi_moon_next, which matters given the crowded sibling set.

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% and the only parameter, 'tanggal', is fully documented in the schema including the YYYY-MM-DD format and today-default. The description adds no format or constraint detail beyond that, so the schema does the heavy lifting and 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 uses a specific verb and resource ('Get the moon phase') and enumerates the returned fields (illumination, phase name ID/EN, age, lunar distance), so an agent knows exactly what comes back. It does not, however, distinguish itself from the sibling astronomi_moon_next, which likely covers upcoming phases.

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 'given a date' framing plus the schema's default-to-today note tells the agent this is the single-date lookup. There is no explicit statement of when to prefer this over astronomi_moon_next or other astronomi tools.

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