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

Annotations only give the generic safety profile (readOnlyHint=false, destructiveHint=false), so the description carries most of the load. It discloses non-obvious behavior: null=none, 0=stop today, that over-cap recipients wait for later days, and that the cap applies in the account timezone. It doesn't explain reversibility or auth/permission requirements, but the added context is substantial.

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?

The definition is dense but well front-loaded, opening with the resource, then get semantics, then set semantics, then usage. Most sentences earn their place, though the get/set token lists are tightly packed and could be marginally cleaner.

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 no output schema, the description helpfully enumerates what get returns, and it covers behavior and value semantics for all three parameters. Given no output schema exists it is nearly complete; only auth/permission context and the read/write split of the mixed get/set action are left unstated.

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 67%, and the description meaningfully extends it: it clarifies the two get/set actions, that 'domain' scopes to one domain vs account-wide, and the null/0 semantics of daily_email_send_cap. It also documents the get return values (cap, sent_today, remaining_today, domain_caps), which the schema does not cover.

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 states a specific resource (daily cap on campaign EMAILS) and explicitly disambiguates it from the sibling SMS tools with '(not SMS)'. It also spells out both get and set behaviors, so an agent can tell exactly what this manages without opening the schema.

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 a concrete use case ('Use to warm a new domain (~20/day)') and implicitly routes email-cap concerns here rather than to sms_send/sms_optouts. However, it doesn't state explicit when-not conditions or the exact prerequisite for setting a domain cap beyond the parameter description.

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