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

With no annotations, the description carries the full burden and does well: it states the tool is free (no credits required), requires proof of npub ownership to prevent enumeration, and clarifies this is a balance check rather than a write operation. It doesn't disclose failure modes or rate limits, but the disclosed behaviors are valuable.

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 three short paragraphs with the main purpose front-loaded. Each sentence earns its place: purpose, distinction from alternative, and cost/auth requirements. No wasted words.

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 only 2 parameters and the presence of an output schema, the description covers all essential context: what the balance represents, when to use this tool vs the sibling, cost implications, and authentication requirements. This is sufficient for an agent to select and invoke the tool correctly.

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 the schema already includes detailed descriptions for both npub and dpop_token (including dpop_token format and constraints). The description adds no parameter-specific details beyond what the schema provides, so baseline 3 is appropriate.

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 clearly states 'Check a patron's credit balance at this operator' with a specific verb and resource, and explicitly distinguishes it from the operator's own balance tool by naming the alternative. This makes the tool's purpose unambiguous and differentiates it from siblings like brain_check_authority_balance.

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?

The description provides explicit guidance: 'For the operator's own balance at the Authority... use authority_check_balance instead.' It also explains the context of the patron's spending balance and notes the tool is free and requires proof of npub ownership, giving clear when-to-use and cost/auth context.

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