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 fully covered. The description adds genuine value by disclosing the computation source (Swiss Ephemeris) and the exact data points returned, but says nothing about time basis, timezone, or precision.

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 core concept ('de stand van de hemel nu') and then lists the return contents. Nothing is redundant, though the colon-separated list gets slightly dense.

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?

With no parameters and no output schema, the description carries responsibility for describing return values, which it does by enumerating the four data categories. Only a note on the time basis (server time vs. UTC) and geographic assumptions would make it fully complete.

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 tool takes zero parameters, so there is no parameter semantics to explain and the baseline of 4 applies. The schema's additionalProperties:false and empty properties leave no ambiguity for the agent.

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 names a specific resource ('de stand van de hemel nu') and enumerates exactly what is returned: sun/moon sign, moon phase, retrograde planets, and next full/new moon. That makes it clearly distinct from the horoscope siblings, though it never names an alternative to steer the agent away from them.

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?

The word 'nu' (now) plus 'vandaag' in the title implies this is the current-snapshot tool, so usage is inferable. However, there is no explicit statement of when to pick this over maankalender or daghoroscoop, and no exclusions or prerequisites.

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