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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuine non-annotation context ('Data is not stored', entertainment disclaimer), but it never explains the non-idempotent behavior or what the reading actually returns.

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?

Front-loaded with purpose in the first clause and only three sentences total. The trailing prohibition list is slightly padded — 'no image generation' has no apparent relation to the tool — but nothing is verbose.

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 an output schema present, return values need no explanation, and annotations cover safety; the description supplies input formats, privacy stance, and scope limits. The only gap is the ambiguous 'no partner matching' constraint, which could make an agent hesitate on legitimate use.

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 both parameters document accepted formats ('Aries', 'YYYY-MM-DD') with a not-stored note, so the schema does the heavy lifting. The description only restates the accepted inputs ('two zodiac signs or birth dates') without adding format or edge-case detail.

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 ('compare') and resources ('two zodiac signs or birth dates') plus the method used ('astrological aspects, elements, and modalities'), which tells an agent exactly what the tool produces. Siblings (feedback/index tools) are entirely unrelated, so no differentiation is needed.

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?

'Entertainment and reflection only' implies the intended context, and the exclusions (no relationship coercion, no image generation) frame misuse boundaries. However, 'no partner matching' is confusing for a tool whose core job is comparing two people, and no alternatives or preconditions are named.

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