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

Annotations already declare readOnly, idempotent, non-destructive, so the safety profile is covered. The description adds genuinely new behavioral context beyond the schema: per-call cost ($0.001 USDC via x402 on Solana) and an alternate HTTPS endpoint, both of which matter to an agent deciding whether and how to call it.

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 is front-loaded with the semantic meaning and examples, then bounds, then payment/endpoint details. Every sentence contributes — nothing is padded or repeated from the schema.

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-parameter integer function with no output schema, the definition supplies semantics, domain bounds, examples, cost, and an alternate transport. The only mild gap is the absence of explicit sibling disambiguation, which is minor given the self-describing name and examples.

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 the load — and it does, defining the meaning of n (factorial-base digit count), its valid domain (0 to 999999999999999), and concrete example values, compensating for the missing schema descriptions.

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 computable quantity — the number of factorial-base digits of n, including the 0! place — and the worked examples (0→1, 5→3, 23→4, 24→5) pin down the counting convention unambiguously, which is exactly where siblings like factoradic_digit or factoradic could be confused.

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 only implied: the description makes clear this computes a length for a given n, but it never says when to pick this over factoradic, factoradic_digit, or factoradic_decode. No exclusions or routing guidance are offered.

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