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

Annotations already declare readOnlyHint=true, idempotentHint=true and openWorldHint=false, so safety and determinism are covered structurally. The description adds non-obvious domain behavior: plan credits are spent first, pack credits never expire, and the period end is reported. It does not mention caching/staleness of the balance, which is the one useful behavioral fact still missing for a read tool.

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?

Content is front-loaded: the return contents come first, then the spending rules, then the call trigger. The first sentence is long and comma-chained, and stray indentation whitespace slightly hurts readability, but no sentence is 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?

With an output schema present, an annotated read-only profile, and zero parameters, the description fills exactly the remaining gap: what the numbers mean and when to fetch them. Nothing an agent needs to call this correctly is absent.

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 for this dimension is 4. The description correctly implies an account-scoped, argument-free read and raises no ambiguity about inputs.

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 resource: "How many Hookbird credits this account has left", then names the exact components returned (plan credits, pack credits, total, monthly allowance, period end). An agent can distinguish it from studio_formats (prices) and studio_generate (spending) without opening any 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?

Gives explicit triggers: "Check this before a large generation or when the user asks about credits." It also explains the economy that motivates the check — Studio generations spend credits while hooks, brand, plans, Radar and benchmarks are free — so the agent can infer when a credit check is warranted.

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