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 is covered. The description adds the group category and a 10-credit cost, which are useful operational facts, but does not add auth, rate-limit, or return-behavior detail. It does not contradict the annotations.

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?

Very concise and front-loaded: the core mapping is stated first, followed by group and cost metadata. No sentence is wasted for a low-complexity lookup tool.

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 simple lookup with rich annotations and an output schema, the description is mostly complete. It could explicitly state that sign is required and what the response contains, but the output schema and enum already cover those needs.

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 67%: fields and precision are documented in the schema, and sign is constrained by an enum. The description only adds that sign is tropical rather than sidereal, which is a modest semantic supplement, but it does not explain fields or precision.

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 mapping: tropical zodiac sign to Elder Futhark affinity rune. This is clear enough to distinguish from generic rune draw tools like astroway_runes_single, though it does not explicitly contrast with siblings.

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 by the mapping: use it when you have a tropical zodiac sign and want its affinity rune. There is no explicit when-to-use, when-not, or alternative guidance; group and cost metadata are not selection guidance.

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