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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description adds meaningful behavioral context beyond that by enumerating what the review actually surfaces (tone, broken links, alt text, spam triggers, accessibility). It still omits return format and any auth/rate-limit notes, so not a 5.

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?

Two tight sentences with zero waste, front-loading the action ('pre-send review on an email's HTML') before the list of what it checks. Every clause earns its place.

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 carries the burden of explaining what comes back; naming the five finding categories largely covers that. For a read-only tool with full schema coverage it is close to complete, with only the return shape left implicit.

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 all four parameters are already documented in the schema. The description adds no syntax, format, or constraint detail for html, subject, audience, or apiKey beyond what the schema provides, making the baseline 3 correct.

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?

The description states a specific verb and resource: 'Run an AI pre-send review on an email's HTML before sending.' It is clearly distinct from send_email or send_campaign_test. It stops short of naming or distinguishing against those specific siblings, so it does not reach 5.

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?

The phrase 'before sending' implies the usage context, so an agent can infer this is a pre-flight check prior to send_email/send_campaign. However, it names no explicit alternative and states no condition for when-not-to-use it (e.g., vs render_email_content or preview_campaign_recipients).

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