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

Annotations already declare readOnly, idempotent, non-destructive, openWorld, so the safety profile is covered. The description adds behavior the annotations cannot: the return type changes to a decimal string past 15 digits, and every call costs $0.001 USDC via x402 on Solana with an HTTPS fallback endpoint. The only gap is that the failure mode for lo > hi is not described.

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 core definition, then constraints, then example, then output format, then payment details — a sensible ordering with no filler. The pricing and HTTPS-endpoint sentence is operationally useful but visually crowds out the semantics; otherwise every sentence earns its place.

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 correctly compensates by telling the agent the return is an integer normally and a decimal string past 15 digits, plus a concrete example result. For a two-integer pure-computation tool this is nearly complete; only error behavior and pagination-free return shape are left implicit.

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 parameter meaning, and it largely does: lo and hi are inclusive indices, both bounded 0..4096, with the ordering constraint 'lo must not pass hi' that appears nowhere in the schema (which only has min/max). It falls short of stating boundary behavior or what an out-of-order call returns.

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?

Opens with a precise verb-and-resource statement: 'The sum of Leonardo numbers from lo through hi inclusive', which tells an agent exactly what is computed and over what range. It includes a worked example (L(0)..L(5) = 34) that disambiguates the indexing convention. It does not name or distinguish itself from the leonardo_index / leonardo_mod / leonardo siblings, so an agent must infer which variant to use from the names alone.

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 rather than stated: an agent can tell this is the range-sum variant of the Leonardo family, and the 'lo must not pass hi' sentence gives a precondition. However, there is no explicit guidance on when to choose this over leonardo_index or leonardo, and no mention of what happens if lo > hi (error vs empty sum) beyond the prohibition itself.

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