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

Annotations already declare readOnly/openWorld/idempotent, and the description adds substantial context beyond them: individual-person entities are refused, results are capped at ~50 curated properties, name lookups are resolved to the best-matching item, and the tool is paid via x402 USDC on Base at $0.002 per successful call, with an unpaid call returning a PaymentRequired object. That is exactly the kind of behavior an agent cannot learn from structured fields.

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 'Use when...' trigger and the entity-refusal rule are front-loaded, which is good. The long enumeration of ~50 property types is somewhat padded but it does concretely demonstrate the return shape, so it earns most of its space; a little trimming would make it tighter.

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?

There is no output schema, so the description carries the full burden of describing returns and does so (field list plus property examples and the ~50-property cap). Combined with the payment model, the person-entity refusal, and ID/name input handling, an agent has everything needed to call it correctly.

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 coverage is 100%, so the baseline is 3, and the description adds meaning on top: it shows the Q-ID format (Q95), explains that a plain name is 'resolved to the best-matching item' (a non-obvious resolution behavior), and clarifies the id-or-q choice. Only 'lang' is left entirely to the schema.

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 a specific verb+resource (retrieve Wikidata entity facts by Q-ID or name) and enumerates the exact payload: label, description, aliases, Wikipedia link, and ~50 curated properties. The phrase 'structured, machine-readable facts rather than prose' directly contrasts it against the prose-oriented sibling 'summary', so an agent can route without opening schemas.

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?

It gives an explicit trigger ('Use when you need structured, machine-readable facts rather than prose') and an implicit contrast with the prose tool. However, it never names the alternatives (search, summary) nor states when-not-to-use, so selection still requires inference from the sibling names.

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