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

No annotations exist, so the description carries the burden. It discloses two non-obvious behaviors: the call is free ('Free — no credits required') and requires proof of npub ownership to prevent balance enumeration. It doesn't explicitly state read-only semantics, but 'Check' plus the free note make the operation's nature reasonably clear.

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 short, front-loaded paragraphs: purpose, distinction from sibling, and cost/auth caveats. Every sentence adds information; no filler.

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 two-parameter tool with fully described schema and an output schema, the description covers purpose, scope, cost, authentication requirement, and the main alternative. The only minor issue is the imprecise sibling name, which does not undermine calling this 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 description coverage is 100%, so the baseline applies. The description adds no new parameter-level detail beyond the schema; the 'proof of npub ownership' sentence reinforces the dpop_token requirement but is already implied by the schema's description.

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?

Opens with a specific verb and object: 'Check a patron's credit balance at this operator.' It then defines that balance as 'patron's spending balance — credits purchased via Lightning for tool calls at this operator' and explicitly distinguishes it from the operator's own Authority balance, so it is not confusable with goodearth_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?

Explicitly states when to use the sibling: 'For the operator's own balance at the Authority ... use authority_check_balance instead.' It also notes the call is free, which is relevant to choosing it. However, the named alternative is not exactly the sibling's name (goodearth_check_authority_balance), introducing a small routing ambiguity.

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