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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds genuinely new behavioral context beyond that: 'Spends nothing,' plus the credit-accounting rules (1 credit = 1 person found, the extra credit for research, and refunds when research fails), which an agent needs in order to reason about costs.

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 returned values are front-loaded in the first sentence, and the cost rules follow as supporting context. It is dense but nearly every clause carries useful product semantics; the credit-cost sentence is somewhat convoluted ('costs 1 credit more' is ambiguous about the reference point) and could be tightened.

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 input parameters and no output schema, the description carries the full burden of explaining what comes back, and it does so concretely (credits left, monthly remainder, pack remainder, renewal day). Combined with the 'Spends nothing' assurance and the cost model, an agent has everything needed to call and interpret it.

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 there is nothing for the description to disambiguate; the baseline applies. The description correctly implies the call is argument-free by describing only returned figures.

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 names a specific verb and resource ('Returns the credits left') and enumerates the exact figures returned: remaining monthly credits, remaining purchased-pack credits, and the renewal day. It is unmistakably distinct from every sibling in the list, none of which deal with credit balances.

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?

It gives clear context for why an agent would call it (to see what budget remains before spending) and explicitly contrasts free actions (drafting notes on the Signals tab, research_signal_lead) against credit-consuming ones. It never states a hard 'use this before X' rule or names a competing tool for the same information, but no such alternative exists, so the gap is minor.

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