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

With no annotations provided, the description carries the full burden of behavioral disclosure and does so well: no rewrites, content-signal-only scoring with no inbox-placement guarantee, pay-per-call pricing, and the error behavior when the payment-signature header is missing. This goes well beyond a basic 'checks deliverability' statement.

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?

The description is compact and front-loaded: the core output and use case come first, followed by the sibling distinction, limitation, and payment specifics. Every sentence adds information, and none of it duplicates the schema.

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?

There is no output schema, so the description correctly specifies the return shape (pass/warn/fail, score, flagged phrases). It also covers payment terms and error behavior, making it complete for an agent to invoke and interpret results without additional context.

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 the schema already documents both query and context. The description only adds that this checks a single email and is content-signal based; it does not add per-parameter syntax or format guidance, matching the baseline for full schema coverage.

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 function: a spam-risk gate for one email that returns pass/warn/fail, a 0-100 score, and up to 3 flagged phrases. It also explicitly distinguishes itself from the analyze-email-deliverability sibling, so an agent can tell the tools apart 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?

It gives explicit when-to-use context: a go/no-go check before sending or bulk screening of many drafts. It also names the alternative (analyze-email-deliverability) for full audits with reasons, subject-line risk, and rewrites, listing what this tool will not do ('No rewrites').

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