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

Annotations only cover the safety profile (readOnly/destructive/idempotent/openWorld). The description adds the critical, non-obvious payment handshake: a 402 + PAYMENT-REQUIRED response, a 0.25 USDC charge, and the need to resend with a PAYMENT-SIGNATURE header. That is exactly the context an agent needs before calling and is nowhere in the 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?

Purpose and usage are front-loaded and efficient, but the description is bilingual with the payment mechanics carried entirely in Japanese. The content earns its place, but the language split hurts scannability for a non-Japanese-reading agent.

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 one-parameter tool with no output schema, the description covers what is returned (cited URLs, findings, gaps), the cost, and the payment flow. Only the pagination/length limits of the brief and any failure modes beyond the 402 are unstated.

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% with a single required parameter, so the schema already documents the field. The description repeats the same constraint ('5-400 chars, any language') without adding format, encoding, or example guidance, so the 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 ('Returns a one-page research brief with cited source URLs, key findings and open gaps') and names the concrete input shape. An agent can distinguish it from buy_code_review and buy_data_clean without opening either schema.

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?

Gives clear selecting context: 'Call it when an agent needs a sourced answer instead of an unsourced guess.' It does not, however, name or exclude any sibling tool, so the agent still has to infer when a code-review or data-clean brief is the better buy.

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