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

With no annotations, the description carries the full burden, and it delivers: it discloses explicit payment, idempotent retries ('Same pass in retries recovers the same purchase'), no auto-renewal, separate tariffs for other categories, and the usage headers X-API-Pass and X-API-Credits-Remaining. No annotation contradiction exists.

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?

Four sentences, each carrying a distinct fact: price/validity, payment requirement, idempotency/no-renewal, exclusions, and usage headers. The most decision-relevant information is front-loaded, with no filler.

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 purchase tool with a fully-described 4-parameter schema and no output schema, the description covers cost, validity, prerequisites, idempotency behavior, exclusions, and how the purchased pass is used. Nothing an agent needs to call or understand the effect of the tool is missing.

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. The description adds behavioral meaning beyond the schema, particularly for api_pass: idempotent recovery on retries and its later use as X-API-Pass. It doesn't add syntax details for payment, transaction, or credit_token, but the schema already documents those.

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 states a specific action and resource: 'Buy 1,000 basic data reads for US$1, valid for 30 days.' It also differentiates scope by noting that 'OCR, AI, documents and delivery keep their own tariffs,' so an agent can tell this purchase bundle apart from related endpoints.

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 clearly establishes the purchase context and the required precondition ('Requires explicit payment'), and tells the agent what is not covered by this purchase ('OCR, AI, documents and delivery keep their own tariffs'). However, it doesn't name an alternative tool or an explicit when-not-to-use condition beyond those excluded tariff categories.

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