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

Annotations already declare readOnlyHint=false, idempotentHint=false and destructiveHint=false. Beyond that, the description adds real behavioral context: the $49 USDC charge, the delivery of a prepaid API key plus 30 days of credit usable on REST and MCP, and the notable billing guarantee that a fully UNKNOWN answer is never charged. It does not cover refunds or what happens on repeat purchase of the same county, so it is not a 5.

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 description is front-loaded with price and pack contents, then adds verification and billing behavior, then a pointer to check_coverage. It is dense and mostly earns its space, though the $49 price appears twice.

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?

This is a paid mutation with no output schema, yet the description never says what the caller actually receives (key value, expiry, credit balance) or what errors a purchase might raise. Combined with the undocumented 'label' parameter, the definition is adequate but leaves real gaps for a tool that spends money.

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 carries the full burden. 'One covered county' gives some meaning to 'jurisdiction', but the 'label' parameter is entirely unaddressed in both schema and description despite its 120-character constraint. The gap is significant for a two-parameter payment tool.

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?

The description leads with a specific verb and resource: 'Buy a $49 county pack: a prepaid API key plus 30 days of jurisdiction credit for one covered county.' This is concrete enough that an agent knows exactly what the tool produces. It does not explicitly distinguish itself from siblings like create_api_key or topup_credits, which is why it falls short of a 5.

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 purchase framing, and the description does route the agent to check_coverage for per-jurisdiction data dates. However, it never says when to choose this over create_api_key or topup_credits, nor does it state prerequisites such as holding USDC or an existing account.

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