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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=false and destructiveHint=false, so the safety profile is covered. The description's 'deterministic' reinforces the idempotency claim and the metadata block adds useful operational context (cost of 10 credits, POST endpoint). It does not, however, describe what the date input does when omitted or the shape of the reading returned.

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 terse and front-loaded: the core capability leads, followed by a compact bracketed metadata block for group, endpoint and cost. No filler sentences. It is arguably too terse, but nothing is wasted.

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 plus the cost/endpoint block cover operations. What is missing is the behavior of the `date` parameter (format, default-to-today semantics) and any routing signal among the five I Ching siblings, which is the main completeness gap for this tool.

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?

The description adds no parameter information whatsoever, and coverage is 67% because the primary `date` parameter has no schema description and is not marked required. The agent is left guessing the date format and whether omitting it yields today's hexagram, which the description could easily have clarified. Only `fields` and `precision` are documented, and that documentation comes from the schema, not the description.

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 the resource (hexagram) and its distinguishing scope ('per-date', 'deterministic'), which separates it from siblings like throw_coins (random) and by_question. It is a noun phrase rather than a verb+resource, and it never names the sibling alternatives explicitly, so an agent must infer the distinction rather than read it.

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?

No when-to-use guidance and no mention of the four sibling I Ching tools (astroway_iching, astroway_iching_by_question, astroway_iching_throw_coins, astroway_iching_lookup_number, astroway_iching_with_changing_lines). The 'per-date' qualifier only implies a daily use case; nothing tells the agent when this is preferable to the generic or question-based variants.

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