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

Beyond the read-only/idempotent annotations, the description discloses the return-type switch (decimal string past 15 digits), an input precondition that triggers failure, and the operational cost model ($0.001 USDC per successful call via x402 on Solana) along with an equivalent HTTPS endpoint. This is exactly the payment/auth and output-shape context annotations cannot convey.

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?

Six short sentences, each carrying distinct information: semantics, example, precondition, domain, return format, and access/cost. The core definition and constraint are front-loaded before the commercial details.

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 two-integer, no-output-schema tool with annotations already declaring the safety profile, the description covers everything an agent needs: what is computed, the valid domain, the ordering constraint, and how the result is serialized. Nothing material is missing.

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 must carry the load, and it does: lo and hi are indices into the hexanacci sequence, the valid domain is 0–512, and lo <= hi is required. It still doesn't say whether the sum is inclusive of both endpoints (only the example implies it), which keeps it from a 5.

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 verb and resource — the sum of hexanacci numbers over an inclusive index range — plus a worked example (H(0)..H(10) = 32) that pins down the convention. That implicitly separates it from siblings like hexanacci, hexanacci_step, and hexanacci_mod, though none are named explicitly.

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: an agent can infer this is the range-sum tool rather than the single-term tool, and a precondition ('lo must not pass hi') is given. But there is no explicit statement of when to prefer it over hexanacci/hexanacci_index, and no exclusion guidance.

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