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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds non-obvious context beyond that: rendering uses sample data, and an email containing errors causes the default email to be sent instead. Those are meaningful behavioral facts not present in the annotations.

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?

A single front-loaded sentence carrying the action first and the returned fields after. It is compact with no filler, though the trailing list and parenthetical make it slightly dense for one sentence.

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 must convey what a preview returns, and it does list subject, errors, warnings, and plain text. Parameters are covered by the schema, and the safety profile by annotations, so the remaining gaps are minor.

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 the enumerated 'kind' are already fully documented by the schema. The description lists rendered outputs (subject, errors, warnings, plain text) rather than clarifying either parameter, so it adds nothing beyond the schema and the baseline 3 applies.

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: 'Render the saved email with sample data', which clearly separates it from sibling reads like get_site_email (fetch raw data) and update_site_email (mutate). It does not explicitly name those alternatives though, so the differentiation is implied rather than stated.

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?

There is no when-to-use guidance, no mention of prerequisites, and no routing to alternatives such as get_site_email or update_site_email. An agent can infer this is a dry-run preview, but nothing in the text tells it when previewing is the right call versus fetching or editing.

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