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

Beyond the annotations (readOnly, idempotent), the description discloses real behavioral constraints: coverage is limited to 2026 and 2027, times are in Dutch time, and each entry includes zodiac sign. That is meaningful context an agent cannot get from the structured fields.

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 that front-loads the resource, then the year range, the output fields and the timezone. No filler or redundancy.

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 read-only, zero-required-param lookup with no output schema, the description covers scope, year restriction, timezone and returned fields. Only minor gaps remain, such as behavior for out-of-range months, which is a small omission.

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 the JJJJ-MM pattern and the 'empty means current month' default already documented in the schema. The description's 'in een maand' merely restates the month scope and adds no format or edge-case detail, so 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?

States a specific resource (volle en nieuwe manen) scoped to a month, plus the data returned (datum, tijd, sterrenbeeld). That clearly separates it from hemel_vandaag, maandhoroscoop and the other siblings, though it never names an alternative.

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: consult moon phases for a given month. No explicit when-to-use / when-not-to-use guidance and no pointer to hemel_vandaag for a single-day view, so an agent must infer the routing.

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