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

Annotations already cover safety (readOnly, idempotent, non-destructive), and the description goes beyond them with genuinely operationally relevant facts: a monetary cost of $0.001 USDC per successful call, x402/Solana payment, and an equivalent HTTPS endpoint. It does not state failure behavior for out-of-range n or whether paid failed calls are charged, but the cost and payment model disclosure is exactly the kind of context annotations cannot carry.

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-loaded with the definition, then definitional clarification, then examples, then domain and pricing — a logical order with no filler. The endpoint URL and price are essential for an x402 tool, though the definitional sentence and the example list are slightly redundant with each other.

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, no-output-schema tool this covers domain, return type (via examples), cost, and transport alternative, so an agent can call it correctly and knows the monetary consequence. The only gap is unspecified behavior at out-of-range or invalid n, which is minor given the stated bounds.

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%, so the description carries the burden, and it does state the valid domain of n (1 to 1e12), which is the only parameter constraint that matters. The value examples (1→1, 6→12, 12→20, 30→72) also implicitly confirm n is a plain integer and what the return value looks like.

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?

Names a precise mathematical function (sum of unitary divisors of n) and defines the term inline, which matters in a sibling set full of near-neighbors like unit_sum, unitary_count, biunitary_sigma, and infinitary_sigma. It never explicitly says which sibling to prefer when the intent is adjacent, so differentiation is definitional rather than routing.

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?

Usage is implied by the domain bound (n from 1 to 1e12) and the worked examples, which tell an agent the tool fits single-integer evaluation rather than range or counting queries. There is no explicit when-to-use/when-not guidance and no mention of unitary_count or biunitary_sigma as alternatives for related intents.

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