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

Annotations already declare the full safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), so the description carries a low burden. It adds the useful billing fact '[Cost: 10 credits (Tier 1)]', which is genuinely behavioral and not derivable from annotations, but discloses nothing about latency, auth, or output beyond the endpoint path.

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?

The core mapping is front-loaded in the first line, and the bracketed metadata is densely packed with no filler. Structure is efficient, though the tagged metadata lines are more template scaffolding than prose that earns its place.

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?

An output schema exists, so return values need not be described, and annotations cover the safety profile, freeing the description to focus on identity and cost. The one missing piece for a genuinely complete definition is sibling disambiguation among the other rune tools.

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 description coverage is 67%; the two optional parameters (fields, precision) are documented in the schema itself, and the required 'sign' is self-documenting via its 12-value enum. The description only restates that sign is required and adds no format or semantics beyond the schema, so the 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 telegraphic line 'Tropical-sign → Elder Futhark affinity rune' names a concrete input (tropical zodiac sign) and a concrete output (Elder Futhark affinity rune), so the mapping is unambiguous. It does not differentiate itself from the rune siblings (runes_single, runes_three, runes_nine), which is the only gap keeping it from a 5.

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?

There is no when-to-use / when-not-to-use guidance and no routing to or from any sibling rune tool. The only contextual signal is '[Required: sign]' and cost, which are invocation facts, not usage guidance.

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