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

Annotations already cover read-only, idempotent, non-destructive, so the bar is lower, yet the description adds real context the annotations do not: per-call cost ($0.001 USDC via x402 on Solana), a failure mode (unmakeable amounts rejected), and an alternate HTTPS endpoint. It stops short of saying whether a rejected amount raises an error or returns a sentinel value.

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?

Core purpose leads, the example immediately disambiguates the return value, constraints follow, and commercial/transport details are pushed to the end. No sentence is filler, including the pricing line, which an agent needs before paying for a call.

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 three-integer pure function with no output schema, the description supplies semantics, bounds, an example, and the impossible-input case, which is nearly everything needed. The only residual ambiguity is the exact shape of the rejection (exception vs. null) and whether a coin multiset is ever returned.

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 full burden; it does so by naming the roles (a and b as denominations, n as the target sum) rather than leaving three bare integers. The stated bounds duplicate the schema's minimum/maximum, which is redundant but harmless.

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 computation (minimum number of coins of denominations a and b summing to n) with a worked example that pins down the return value as a count. It is distinguishable from near-siblings like coin_ways, coin_check, and mcnugget_min on the strength of the wording alone, though no sibling is 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 implied by the example and the note that impossible amounts are rejected, but there is no explicit statement of when to pick this over coin_count/coin_ways/mcnugget_min or what preconditions apply. The agent can infer the case, but must do the routing itself.

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