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

With no annotations, the description carries the full burden and does so well: it discloses that an unsubscribe link is auto-appended, that invalid/role/blocked/unsubscribed recipients are skipped at no cost, that each accepted recipient consumes 1 email of the daily allowance, and that an oversized campaign is refused atomically. It omits auth requirements and any rate-limit detail beyond the allowance.

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 dense sentences with zero filler, front-loaded with the core action and recipient limit, then the billing and failure semantics. Every clause carries actionable 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?

For a 6-parameter mutation tool with no annotations and no output schema, the description covers the critical behavioral surface (cost accounting, skip rules, atomic refusal, auto-unsubscribe). It stops short of describing auth/permission requirements or the response, which the absent output schema leaves unaddressed.

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 description coverage is only 50%, so the description should compensate, but it only restates the recipient cap (already in the schema) and alludes to unsubscribes without explaining list_id. Nothing is said about from, html, text, subject, or how html and text interact, leaving half the parameters unexplained in both places.

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 verb and resource plus scope: "Send a marketing email to up to 1,000 recipients." The batch limit and campaign semantics clearly distinguish it from the single-send sibling send_email without needing to name it.

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?

Usage context is implied rather than stated: the 1,000-recipient cap and the daily-allowance accounting tell the agent this is the bulk path, but there is no explicit "use this instead of send_email" or when-not-to-use guidance. The refusal rule gives useful preconditions but not alternatives.

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