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

Annotations already declare readOnly, idempotent, and non-destructive behavior, so the description's main added value is the pricing model ($0.001 USDC per successful call via x402 on Solana) and the alternate HTTPS endpoint. That is genuine operational context not present in the structured fields, though it doesn't discuss rate limits or error behavior.

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 core semantics and worked examples are front-loaded in the first three sentences, with operational metadata (price, endpoint) trailing. No sentence is wasted, though mixing pricing text into a math tool description slightly dilutes the focus.

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 single-integer tool with no output schema, the examples effectively communicate the three-part return value (prime, next prime, gap) and the valid input range. The remaining gap is the absence of any statement about failure modes or how the x402 payment requirement affects invocation flow.

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 0%, so the description must carry parameter meaning, and it does: the examples show exactly how n is interpreted (floor prime, successor, difference) and the range 2–10,000,000 is restated alongside the schema. It stops short of stating what happens at a boundary such as n=2 or non-prime edge cases.

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 computation: the prime at or below n, the next prime, and the gap between them, backed by two worked examples (n=10 → 7/11/4, n=11 → 2). This clearly distinguishes it from siblings like next_prime, prev_prime, or prime_check, which return a single prime or a boolean rather than a gap pair.

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 domain (n from 2 to 10,000,000) and examples imply when the tool is applicable, and the sibling list includes obvious near-misses (next_prime, prev_prime, twin_prime), but the description never explicitly routes the agent to or away from any alternative. An agent must infer selection.

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