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

Beyond the annotations (readOnlyHint=false, destructiveHint=false), it discloses that nothing is sent at this stage, that the sender domain must be verified, that a paid account is required, and that there is a 200-campaign account cap. Those are exactly the prerequisites and limits an agent needs before attempting a write.

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?

Every sentence earns its place: write intent first, non-sending guarantee second, workflow third, prerequisites fourth, endpoint last as reference. No filler or repetition of the schema.

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?

Workflow, prerequisites, limits and the underlying endpoint are all covered for a schema-only tool with no output schema. The one minor gap is that it never says the call returns a campaign identifier, which the agent needs in order to pass it to assign_campaign_recipients.

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%, so the schema already explains name, reply_to, content_html and sender_email. The description reinforces the verified-domain constraint on sender_email but adds nothing about the two undocumented fields (subject, sender_name), so it neither compensates for nor extends the schema meaningfully.

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 and resource ("create a campaign DRAFT") plus an explicit scope qualifier ("Nothing is sent") that separates it from enginemailer_send_campaign. An agent can distinguish it from every sibling without opening a 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?

Gives the exact ordering: create draft here, assign recipients with enginemailer_assign_campaign_recipients, then send with enginemailer_send_campaign. It names both alternatives and the condition that selects each, leaving nothing to inference.

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