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

Goes well beyond the readOnly/openWorld annotations by disclosing the commercial model: 3 free calls per day across all tools, then $0.005 USDC via x402 or card credits, with payment passed in-band at params._meta["x402/payment"]. That is operationally critical context an agent cannot get from any structured field, though it says nothing about failure behavior when payment is absent or about result caching.

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 payload and the pricing model are stated up front, and the fact list is compact rather than prose-heavy. There is mild redundancy in restating 'wiki-fact' by name in the 'When to use' sentence, but nothing is wasted at length.

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, the description need not explain return values, and it is complete on inputs, scope (any language), and cost. The only remaining gap is what the agent should expect when the free quota is exhausted or payment is not attached.

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 the schema already documents 'q' and 'lang'. The description only adds the loose hint 'Any Wikipedia language', which marginally reinforces the lang parameter but adds no format or constraint 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?

States a specific verb and resource ('Wikipedia fact lookup') and enumerates the returned payload (summary, description, URL, Wikidata facts). It is distinguishable from generic grounding siblings like company_profile or entity_extract by its Wikipedia/Wikidata basis, though it never names those alternatives explicitly.

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?

The 'When to use' line gives a concrete trigger: grounding an entity with summary plus structured facts such as founded, HQ, CEO, website. It provides clear positive context but no exclusions or named alternatives for when a different grounding tool is preferable.

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