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 covered. The description adds genuinely useful operational context the annotations do not carry: the endpoint (POST /v1/runes/nine) and the cost (10 credits, Tier 1). It says nothing, though, about whether the cast is randomized or seeded, which matters given the optional `seed` parameter.

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?

It is short and front-loads the purpose line, but three of the four lines are bracketed boilerplate metadata (group, endpoint, cost) rather than information about the tool's behavior. Nothing is wasted exactly, yet the content density is low.

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. But for a 5-parameter divination tool with 40% schema coverage and no usage guidance, the description leaves too much for the agent to infer — especially what `seed`, `question`, and `allowReversed` do and when a nine-rune spread is appropriate versus the one- and three-rune siblings.

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 only 40% — only `fields` and `precision` are documented, and those read as generic response-shaping options. The domain-critical parameters (`seed`, `question`, `allowReversed`, which governs reversed-rune outcomes) have no schema description and no explanation in the tool description either. The description does not compensate for the coverage gap.

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?

"Pennick layout 9-rune cast" names a specific resource (a 9-rune spread in the Pennick layout), which is enough to distinguish it from astroway_runes_single and astroway_runes_three by count. However, the verb is only implied ("cast") and the description never says what the operation actually does — draws nine runes into a positional spread and interprets them. It is a label, not a purpose statement.

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 guidance on when to choose this over astroway_runes_single, astroway_runes_three, astroway_runes_runes, or astroway_runes_by_zodiac. The only implicit signal is the number 9 in the name, which the agent must infer means a larger spread than the siblings.

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