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

Annotations already cover read-only, idempotent, and non-destructive traits, but the description adds real value beyond them: it is unmetered (no credit cost to call) and the no-key path returns 'anonymous unique-per-day remaining — not a wallet,' which warns the agent the value has different semantics per auth mode. It stops short of describing reset/grant timing details.

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 clauses, front-loaded with the core action, with the two behavioral caveats (unmetered, anonymous mode) packed into single phrases. No wasted sentences.

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?

With no output schema and no parameters, the description must carry the return-value burden; it explains the wallet-vs-anonymous distinction well but does not name the concrete fields returned or whether grant reset timing is included. Minor gap for an otherwise trivial call.

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?

The tool takes zero parameters, so the baseline is 4. The description correctly implies no inputs are needed and instead frames the one implicit input that matters — the presence or absence of an API key — which meaningfully changes the result.

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 and resource ('Show remaining Census credits') plus the scoping subject ('for this API key'), which no sibling tool covers. An agent can identify this as the credits/balance tool without opening the schema.

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 context is implied rather than stated: 'Unmetered' signals it is free to call and the two auth modes are distinguished, but there is no explicit when-to-use vs. when-not guidance or reference to alternatives. Adequate for a single-purpose balance check, but nothing routes the agent explicitly.

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