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

Annotations already establish readOnly, idempotent, non-destructive, closed-world behavior, so the bar is low. The description adds two genuinely useful facts beyond them: that output is deterministic (same question yields the same hexagram) and that the call costs 10 credits at Tier 1, which is real budgeting context.

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 functional sentence is front-loaded and there is no filler prose. The bracketed metadata lines are terse and skimmable, though they read as structured tags rather than prose that earns every word.

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, leaving the definition adequate for a one-required-param tool. The gap is the unelaborated 'deterministic' claim and the absence of any sibling routing, which matters given how crowded the I Ching family is.

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%: `fields` and `precision` are already documented in the schema, and `question` is self-evident. '[Required: question]' merely restates the schema's required array, adding no syntax or constraint meaning beyond it, so 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 first sentence gives a specific verb (derive) plus resource (hexagram) and names the input (question text). 'Deterministic' meaningfully separates it from the random astroway_iching_throw_coins sibling, but no sibling is named explicitly, so an agent must infer the distinction.

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, or alternative routing guidance despite five closely-related I Ching siblings (daily, lookup_number, throw_coins, with_changing_lines, plain iching). The agent is left to guess which variant fits its intent.

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