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

With no annotations, the description carries the full burden and does disclose useful behavior: unknown or missing code returns ok false, plus a pricing/free-trial note. However, it omits expected code casing/normalization and the success response shape, which matter for a zero-annotation tool.

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?

A single front-loaded sentence covering purpose and edge-case behavior, followed by a short pricing note. Efficient, with only the emoji pricing clause adding marginal noise.

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 trivial lookup with no output schema, the core purpose and error behavior are covered. The unresolved three-parameter ambiguity (code vs lang vs input, with none required) is the main completeness gap.

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 0% across three parameters. The description explains 'code' (two-letter language code) and its missing-value behavior, but 'lang' and 'input' are left entirely unexplained, leaving the agent to guess whether they are aliases or independent inputs.

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: 'Returns the English language name for a two-letter language code.' An agent can distinguish this from siblings like x402-language-by-country or x402-script-detect, though no sibling is named 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 description implies usage (you supply a two-letter code) and documents the failure condition for unknown/missing codes, but it never states when to prefer this over alternatives such as x402-language-by-country or x402-ai-language. Usage is inferable but not explicit.

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