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

With no annotations supplied, the description carries the full behavioral burden and does well: it discloses paid access at $0.05 USDC per call via x402 through _meta["x402/payment"], and that sample=true yields a free 3-row preview. That pricing and preview behavior is exactly the kind of context an agent cannot get from the schema. It does not describe rate limits, error behavior, or result ordering/pagination semantics for /answer, which keeps it from a 5.

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 purpose and scope are front-loaded in the first sentence, followed by ranking criteria, then routes and payment mechanics in descending order of importance. It is dense and the middle sentence packs several metrics into one clause, but no sentence is filler. Minor density cost keeps it at 4 rather than 5.

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?

For a 3-parameter tool with a nested free-form params object and no output schema, the description supplies the missing pieces an agent needs: what is ranked, by what criteria, which routes exist and their query parameters, and the payment/preview mechanics. The main residual gap is return shape and how pagination behaves on /answer, which matters somewhat given the absence of an output schema. Overall adequate-to-strong for this complexity.

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 route, params, and sample, establishing a baseline of 3. The description does add some meaning by mapping query parameters to specific routes (/answer takes have, limit, offset; /scripts takes rtl, limit), which the schema's generic params example does not convey. That added mapping is useful but partial, so it does not lift the score above the schema-driven baseline.

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 opens with a specific question-style verb phrase and resource: ranking 60 candidate languages for localization 'beyond en ja zh es pt fr de ko hi ar', which implicitly separates it from the plain 'languages' sibling by scope. It also states the ranking criteria (CLDR speakers, GDP PPP, digital-marketplace reach, official-language countries, CLDR coverage), so an agent knows exactly what this returns. It stops short of naming the sibling tool it complements, so a 4 rather than 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?

The opening question implies the use case (deciding which locales to add next), and the route list plus 'set sample=true for a free 3-row preview' gives practical invocation guidance. However, there is no explicit when-not-to-use guidance and no named alternative such as the 'languages' sibling for the already-supported top-10 locales. Usage is inferable but not stated.

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