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

Annotations already declare read-only, idempotent, open-world, non-destructive behavior. The description adds useful context beyond those annotations: pricing per successful x402 call, the HTTPS endpoint, and sample count thresholds that illustrate outputs.

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?

Front-loads the purpose, then provides examples, valid range, pricing, and endpoint. The examples and payment details are relevant for a paid x402 counting tool, and there is no wasted text.

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 count tool with no output schema, the description provides the valid range, sample outputs, and access/payment details. A brief definition of vampire numbers or an explicit statement that an integer count is returned would make it fully self-contained.

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%, but the description explains n as an inclusive upper bound ('at most n') and gives threshold examples, compensating for the missing schema descriptions. It could define 'vampire number' more explicitly, but the single parameter is otherwise semantically clear.

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 counting operation and scope: how many vampire numbers are at most n. The 'count' framing distinguishes it from siblings like vampire, vampire_next, and vampire_fangs, though it does not explicitly name alternatives.

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?

No sentence says when to choose this tool over vampire, vampire_fangs, vampire_low, or vampire_next. It gives a valid n range and sample thresholds, but those are parameter/behavior details rather than usage guidance.

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