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 fully covered. The description adds genuinely useful non-annotation context: the HTTP endpoint, the group, and a cost caveat ('see your plan — endpoint not in the public credit manifest'). That cost/pricing note is the one real behavioral addition; no rate limits or result-shape notes beyond that.

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 first sentence is front-loaded and complete, and the bracketed metadata lines are dense, scannable and free of filler. Minor redundancy between 'Fetch hexagram 1-64' and '[Required: number]' / the schema's 1-64 range, but overall tight.

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 semantics. Endpoint, group, required parameter and a cost caveat are all supplied. The only real gap is the absence of any routing hint among the many I Ching 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 100%, so 'number', 'fields' and 'precision' are already documented in the schema with ranges and examples. The description only restates the number parameter as required and King Wen ordered, adding no syntax or format detail beyond the schema. 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 description states a specific verb and resource ('Fetch hexagram 1-64 by King Wen number') with an explicit lookup key and range, which is unambiguous on its own. It does not, however, distinguish this from the five sibling I Ching tools (throw_coins, by_question, daily, with_changing_lines), so it stops short of 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?

Usage is only implied by 'by King Wen number' — an agent must infer that this is the direct-number path rather than a cast/divination path. No alternatives are named despite astroway_iching, astroway_iching_by_question, astroway_iching_throw_coins and astroway_iching_with_changing_lines all being plausible destinations, and no when-not guidance is given.

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