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

With no annotations, the description carries the full transparency burden. It discloses meaningful behavior: new domains start at a low daily cap and climb as they prove themselves, and it reveals whether sending is paused and how many domains the account may hold. It stops short of stating error behavior or caching, but for a read-only limits query it provides solid context.

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 sentences, all substantive: the first states output meaning, the second explains the dynamic cap behavior, and the third gives invocation guidance. No filler or repetition of schema names; information is front-loaded.

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 tool with one optional parameter and no output schema, the description explains the key return concepts: daily cap, graduation trigger, account standing, paused status, and the difference between domain-level and account-level calls. This is enough for an agent to select and invoke it correctly without additional context.

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 schema already documents 'domain' as optional with 100% coverage. The description adds practical nuance by clarifying that omitting the domain returns account-level limits while including it returns the domain's allowance. This goes slightly beyond the schema's wording, earning above baseline.

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 opens with a specific question the tool answers: how much a domain may send today, what raises its cap, and the account's standing (domain count, paused status). This clearly distinguishes it from siblings like send_email or get_delivery_events, which concern sending actions and delivery history rather than limits.

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 provides explicit when-to-use guidance: 'check this before planning a bulk send rather than discovering it part-way.' It also explains the optional parameter behavior: omit domain for account-level answer. It lacks explicit when-not-to-use guidance or named alternatives, but the context is clear enough for a one-parameter read tool.

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