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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds genuinely new behavioral context the annotations do not carry: a per-call price ($0.001 USDC, x402 on Solana) and an alternate HTTPS endpoint for the same operation. It does not describe error handling for out-of-range n, but with annotations present that is a minor gap.

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 definition and examples are front-loaded and every sentence earns its place; the pricing and endpoint sentence is somewhat tangential to invocation but is legitimate operational context. No filler or redundancies.

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?

With no output schema, the description must convey the return value, which the examples do (a scalar integer, with n=1 giving 0). Combined with the declared annotations and the stated input domain, an agent has enough to call this correctly; only explicit out-of-range or error behavior is left 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 description coverage is 0% and the single parameter n has no in-schema description, so the description must carry the burden. It does so reasonably: it states the range (1 to 1,000,000) and the examples make the meaning of n and the return value concrete, including the edge cases n=1 (returns 0) and n prime (returns itself).

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 names a precise arithmetic function ('sum of the distinct prime factors of n') and pins it down with four worked examples (1→0, 8→2, 12→5, 30→10). The word 'distinct' is the key differentiator from the sibling sopfr, which sums with multiplicity, so an agent can distinguish the two even without an explicit cross-reference.

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 definition and examples imply when the tool applies, and the domain restriction (1–1,000,000) is stated, but there is no explicit routing guidance such as 'use sopfr if you want multiplicity' or a note on what happens outside the range. For a pure numeric function the function definition carries most of the selection burden, which is why this lands at adequate rather than poor.

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