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 genuinely new operational facts (POST endpoint and 10-credit Tier 1 cost) that the agent cannot get from annotations, but says nothing about determinism of the cast, how seed affects results, or what happens with an omitted question.

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?

Extremely tight and front-loaded: the spread meaning comes first, followed by compact metadata lines. Nothing is wasted, though the brevity edges toward under-specification rather than crispness.

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 no explanation, and annotations cover the safety profile. However, with five parameters at 40% description coverage and zero usage guidance, the agent lacks enough to confidently decide when to call this versus sibling rune tools or how seed/allowReversed shape the reading.

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%: fields and precision are documented, but seed, question, and allowReversed carry no schema description at all. The description adds no parameter meaning whatsoever, so it fails to compensate for the uncovered parameters, including the semantically important allowReversed default.

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 the specific spread (Past/Present/Future with the Urdr/Verdandi/Skuld correspondences), which combined with the tool name and 'Elder Futhark Runes' group makes the action identifiable. It implicitly separates this from runes_single and runes_nine via the three-position structure, though it never explicitly states 'performs a three-rune cast.' Clear purpose, but sibling differentiation is left to inference.

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 guidance, no statement of when to prefer this over astroway_runes_single, astroway_runes_nine, or astroway_runes_runes, and no prerequisites. The metadata block gives endpoint and cost but nothing about selection context.

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