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

Adds substantive context beyond annotations: a postal address is mandatory (footer slot or settings.address) and must be requested from the user, merge tags have no fallback and must not follow a greeting, and dry_run performs a validate-and-preview pass. Annotations already cover safety profile, so this extra operational detail is a genuine value-add; response/return behavior after saving is not covered.

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?

Purpose is front-loaded in the first clause, and each following sentence carries distinct, actionable information (build order, catalog resource, address requirement, merge tags, dry_run). It is dense and long-ish, but waste is minimal.

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 deeply nested creation tool with no output schema, the description covers the essential build model, the external catalog dependency, the mandatory postal address, and the dry-run validation path. It stops short of saying what is returned on success or how validation failures surface, which matters for a non-idempotent creation call.

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 a 3 baseline applies, but the description goes further by explaining the row model (layout+columns+blocks vs a ready-made section), the [[key]] merge-tag syntax, and where the address slot lives. That said, it leaves some nested field intent (e.g. layout 'props' vs block 'props') to the schema and catalog resource.

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: 'Design a new email and save it as a template' that lands in Mailercloud's drag-and-drop editor. The 'never send HTML' line implicitly separates it from the HTML-template sibling create_template, but it never names create_template or update_dnd_email_template directly, so sibling differentiation is left to inference.

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 a concrete build order (settings, then rows), names the helper tools/resources to consult (list_email_sections, mailercloud://email-blocks/catalog), and tells the agent to use dry_run:true to preview. It does not state when to prefer this over create_template or when to switch to update_dnd_email_template for an existing template.

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