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 real value beyond that by disclosing the accounting rule that governs the returned allowance — one unit per To/Cc/Bcc recipient, held for 24 hours — which an agent cannot infer from the schema.

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?

Two short sentences with no waste. The core purpose is front-loaded and the quota rule follows as supporting detail.

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, return values need not be explained, and the description adequately covers what the tool reports and how the allowance is consumed. The only gap is routing guidance against get_sending_policy.

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 adds no parameter discussion, and there is nothing further to document.

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 ('Check') and resource ('sending allowance'), with the scope clarified as shared across all the account's inboxes. It does not, however, differentiate itself from the sibling get_sending_policy, which an agent could reasonably confuse with a quota check.

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 quota mechanics ('each To, Cc and Bcc recipient uses one unit for 24 hours') imply the tool is for pre-send capacity checks, but there is no explicit when-to-use statement and no mention of get_sending_policy as the alternative for policy questions.

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