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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, and the description stays consistent, explicitly saying it neither provisions nor orders. It adds genuine behavioral context the annotations can't: the 100-domain cap and MX lookups, the fallback that gateways/self-hosted/no-MX recipients are folded into the Google pool with their share reported, and the no-reserve-capacity assumption. Lacks any note on runtime or lookup failure behavior.

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 purpose and mechanism, and dense with useful detail. The closing sentences on how orders are placed are relevant context but not needed to invoke the tool, so a small amount could be trimmed.

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?

There is no output schema, and the description fully compensates by enumerating what comes back: inbox count, domain count, per-inbox pace and monthly cost per pool, plus totals, plus the 'other' share. An agent can call it correctly and interpret the return without further documentation.

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 every parameter including enums already documents itself; baseline 3 applies. The description only reinforces the `domains` cap and the routing of non-Google/non-Microsoft recipients, which clarifies result interpretation more than parameter meaning.

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 ('Estimates a sending fleet for a recipient list') and immediately explains the mechanism: MX lookups over up to 100 domains feeding Google/Microsoft/other mix and pool sizing. It also draws a hard line against provisioning or ordering, which separates it from ordering-adjacent siblings.

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 one real usage rule — 'For a longer list, send a sample: the estimate follows the provider split, not the list length' — and states it assumes no reserve capacity. But it never says when to choose this over quote_inboxes, plan_rotation, plan_infrastructure, or get_pricing, so the agent must infer the boundary.

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