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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds non-obvious behavior: values are placeholders, the render is recipient-less and tracking-free, and an empty `html` means the campaign has no content yet. The empty-result signal is exactly the kind of behavioral detail annotations cannot convey.

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, front-loaded with the core action, then the workflow, then the edge case. No filler, and the most decision-relevant information (what it renders, when to call it) comes first.

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?

An output schema exists so return shape need not be explained, yet the description still flags the one field that matters for interpretation (`html`) and what an empty value means. Nothing needed to call this 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 description coverage is 100%, so both `id` and `context` are already documented in the schema; the description adds no syntax or sourcing detail beyond what the schema states. Baseline 3 is appropriate when the schema carries the parameter burden.

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?

Specific verb and resource: 'Render a marketing campaign's `content` block tree to HTML with PLACEHOLDER values'. It also explicitly anchors itself against a sibling ('the same recipient-less, tracking-free render preview_signature does'), so an agent can distinguish it from preview_signature without opening schemas.

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 an explicit workflow position: use it to VERIFY layout after create/update_marketing_campaign and BEFORE schedule_marketing_campaign. It also states the follow-up action (read `html`, fix content if wrong), leaving no ambiguity about when this tool is the right call.

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