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

Annotations already cover read-only, idempotent, and non-destructive behavior, so the bar is lower. The description adds genuinely useful context beyond them: a per-call price ($0.001 USDC via x402 on Solana), an alternate HTTPS endpoint, and the important output trait that values past 15 digits are returned as decimal strings rather than numbers.

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 purpose and a concrete example, then constraints, output format, and payment details. Every sentence adds information an agent needs; no filler.

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?

No output schema exists, and the description compensates by describing the return type (decimal string past 15 digits) and giving a sample result. Parameters and payment/transport details are covered. The only real gap is the absence of a formula for a single alternating factorial term.

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 parameter burden. It does explain that lo and hi are indices, that the range is inclusive, that lo must not exceed hi, and that indices run 1..200 (redundant with schema min/max). It does not define what af(k) is for a single index, so an agent cannot verify the per-term definition, and only the worked example hints at it.

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 alternating factorials over an inclusive range, plus a worked example (af(1)..af(5) = 127) that pins down what is being computed. However, it never differentiates itself from near-identical siblings such as alternating_sum, alt_factorial, and alternating_factorial, which an agent could easily pick by mistake.

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?

There is no statement of when to use this tool versus the many sibling sum/factorial tools, and no exclusions. Only implicit usage can be inferred from the range constraint 'lo must not pass hi' and the 1..200 index bound.

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