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 behavioral context beyond that: the quota is per number rather than per organization, resets at a real billing boundary rather than a rolling window, and is consumed only by Turbo Notify traffic, not phone-originated messages.

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?

Front-loaded with the core answer and structured as three short idea blocks (scope, reset semantics, consumption rules). Markdown bolding and backticked field names add slight visual noise but every sentence carries information.

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 no explanation, and the single parameter is fully documented. Remaining gaps are minor: it does not say what the agent should do when the quota is exhausted or whether the call can fail for an invalid alias.

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?

Schema coverage is 100%, so baseline is 3. The description adds meaning beyond the schema by explaining why the single number_alias parameter matters: an organization with three numbers has three separate allowances, which motivates selecting the correct alias.

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: 'Check how much of this number's message allowance is left.' The per-number scoping sentence distinguishes it from organization-wide usage tools, though it never names the closest siblings (get_usage, get_contact_quota) to make the routing explicit.

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 clear context for when the tool is appropriate (checking remaining allowance for a specific number) and clarifies the unit of measurement so the agent picks the right number. It stops short of stating exclusions or pointing to alternatives such as get_usage for aggregate consumption.

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