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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds substantial context beyond that: the full checklist scope, the blocking rule for `error` vs `warning` levels, the `full_access` API key requirement, and that it is not part of the Resend core API.

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, then the return shape, then the blocking rule and auth requirement. The long checklist enumeration is dense but each item adds real value. Minor tightening possible around the parenthetical asides.

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?

No output schema exists, so the description carries the burden of describing return values — and it does: the checklist categories and the `ready` boolean semantics with error/warning levels. Auth requirements and failure behavior are also covered. Nothing needed to call it correctly is missing.

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 0% and the single `id` parameter is undocumented in both schema and description text directly, but the endpoint reference `GET /broadcasts/{id}/readiness` makes it inferable that `id` is a broadcast identifier. That indirect hint is enough to avoid a lower score, but explicit 'UUID of the broadcast' wording is missing.

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+resource ('Check a broadcast before sending') and immediately clarifies it is a SpacePost extension returning a deliverability checklist. This distinguishes it clearly from get_broadcast (fetch data) and send_broadcast (perform the send).

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?

Explicitly frames the tool as a pre-send gate: 'ready is false when any check has level error; POST /broadcasts/{id}/send is then refused'. That tells the agent when to call it and what happens otherwise. It stops short of naming send_broadcast as the follow-up tool or saying when-not to bother running it.

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