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 facts — that the call is free, does not consume credits, and is scoped to the API key's owning account. It doesn't say whether the value is live or cached, which is a minor remaining gap.

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 sentences with zero waste: scope first, cost profile second, recommended usage last. Nothing repeats the title or the schema.

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, annotation-heavy tool this covers what an agent needs to decide and call it. The only soft spot is return shape — there is no output schema, and the description says 'remaining credits' without indicating the unit or whether a plan/quota breakdown comes back.

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 no parameters, so there is nothing for the description to disambiguate; baseline 4 applies. The description correctly makes clear that no account identifier is needed because the API key determines the account.

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?

Names the specific resource (Easy Email Verification credits), the exact scope ('of the account that owns the API key'), and a distinguishing property (free, non-consuming). It is a noun phrase rather than a verb, relying partly on the title 'Get remaining credits' for the action, which keeps it just short of a 5.

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 an explicit trigger: 'Use it before large verifications to check the balance.' That tells the agent when to call it, but it offers no when-not condition and doesn't reference any alternative (e.g., bulk job status endpoints that might also report consumption).

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