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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds useful context about what pricing modes exist and what the rate table contains, which goes beyond the annotations. However, it doesn't disclose details like whether the rate table is exhaustive or how the key id is formatted.

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 a single dense sentence that packs in the key concepts: balance currency, pricing modes, rate table, and API key id. It is front-loaded with the most important fact (balance in USD). It could be slightly more structured, but it earns its length.

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 zero-parameter read-only account tool, the description covers the main output categories: balance, pricing modes, rate table, and key id. Without an output schema, it does a reasonable job of telling the agent what to expect. It could be more explicit about the response shape, but the coverage is adequate for the tool's simplicity.

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 has zero parameters, so the schema provides no parameter semantics. The description compensates by explaining the meaning of the returned pricing fields (pricing.mode, wall_limit_s, per-class prices, metered per second). This is valuable context for interpreting the output, even though there is no output schema.

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 identifies the tool as providing account balance, pricing details, rate table, and API key id. It uses specific nouns and covers the resource scope. It doesn't explicitly contrast with siblings, but the resource (account) is distinct enough among the listed tools.

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 implies this is for checking balance and pricing before creating jobs, but it doesn't explicitly state when to use it versus alternatives. The sibling list includes capabilities and preflight_deck, which could overlap in pricing context, but no explicit routing guidance is given.

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