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

With no annotations, the description carries the full burden and does so well: it discloses that the operation is free, requires proof of npub ownership, and explains the security rationale against enumeration. This goes beyond a simple read operation and gives the agent actionable behavioral expectations.

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 compact and front-loaded: one line for the core action, then a clarifying distinction, then cost and auth constraints. No filler or redundant repetition of schema 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?

Given the output schema exists and the operation is a simple balance check, the description covers all essential context: what the balance is, which sibling tool to use for the other balance type, cost, and authentication. No critical gaps remain.

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 100% and both parameters have detailed descriptions. The tool description adds the context that npub ownership proof is required, which reinforces the dpop_token's purpose, but does not substantially improve on the schema's own parameter explanations.

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 opens with 'Check a patron's credit balance at this operator', naming a specific verb and resource. It immediately distinguishes this from the operator-side balance check by pointing to 'authority_check_balance', making the tool's scope unmistakable.

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 states when to use this tool (patron spending balance) and when not to ('For the operator's own balance... use authority_check_balance instead'). It also notes the free/no-credit requirement, which helps an agent decide cost implications.

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