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

Annotations declare readOnlyHint so safety is covered, and the description adds valuable behavioral context beyond annotations: that an email with errors sends the default instead, and the list of returned sections. Good extra signal for a preview/render operation.

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?

One tight sentence, front-loaded with the action and result. Minor parenthetical reference to the id parameter ('Pass it on every call.' is in schema, not description) keeps it efficient. No wasted words.

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 read-only preview with no output schema and fully documented parameters, the description covers what gets rendered and the error-path behavior. Adequate; an explicit when-to-use note against siblings would complete it.

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 parameters (id, kind enum) are already documented in the schema. The description adds no parameter-specific details beyond the schema. 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 (Render) and resource (the saved email) with sample data, and names the specific outputs (subject, errors, warnings, plain text). This distinguishes it from get_site_email (fetch config) and update_site_email (mutate).

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?

Implied usage is preview/render before sending, but the description never explicitly says when to use it vs get_site_email or list_site_emails. No when-not guidance.

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