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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so safety is covered. The description adds genuinely new behavioral scope in the negative: it 'performs no payee screening or payment decision' and takes no arguments, which prevents an agent from wrongly expecting a decision from it. Return format is left to the output schema.

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?

Three sentences, front-loaded with the identity of the tool and its contents, then routing guidance. Dense but every clause carries routing or scope information; the middle 'optional' clause is slightly redundant with the preceding conditional but not wasteful.

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?

An output schema exists, so return values need not be described. For a zero-argument reference tool with full annotation coverage, the description supplies everything needed to choose it correctly versus its three siblings.

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?

Zero parameters, so the baseline is 4; the description correctly reinforces this with 'Takes no arguments,' matching the empty schema and the 'Example arguments: {}' note. No parameter semantics are needed or missing.

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+resource ('free, read-only service reference') and enumerates the exact content it returns: prices, default spending rules, payment setup, trial allowance, and an example call. An agent can distinguish this from check_payee and preflight_payment immediately.

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?

Explicitly gives when-to-use conditions and names both alternatives with their selecting conditions: 'If you already have a payment challenge or cart, call preflight_payment directly; this reference call is optional' and 'Use check_payee for standalone payee risk.' Nothing is left to inference.

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