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

With no annotations, the description carries the full behavioral burden and does so well: free, keyless, no account, no SMTP ping, one full record versus truncated records for extras. It also discloses the exact output shape for the primary address and for additional addresses, which an agent needs in order to interpret results.

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?

Front-loads the key facts: free, keyless, one full grade. It is dense but well organized, with the main behavior and the upsell/alternative at the end. Slightly long for two parameters, but no sentence is wasted.

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 two-parameter preview tool with no output schema and no annotations, the description supplies everything an agent needs: cost, auth, what is checked, what is returned for one versus many addresses, and where the paid alternative lives. Nothing material about calling or interpreting the tool 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 coverage is 100% and both parameter descriptions already state that email is graded in full while emails' first entry is full and the rest return only {deliverable, grade}. The description reinforces this but adds no syntax, format, or constraint details beyond what the schema already provides.

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 and resource: a free, keyless email-deliverability preview that grades one address in full, with an explicit list of checks (syntax, MX, provider, SPF/DMARC, flags, typo did-you-mean, A–F grade). It clearly distinguishes itself from the paid sibling by naming the full /email/verify endpoint and routing metered access through get_premium_access.

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?

Makes the single-address use case explicit and explains what happens if more addresses are supplied (only {deliverable, grade}). It also points to get_premium_access for the paid, bulk-capable endpoint. It stops short of explicit when-not-to-use conditions beyond that contrast, so 4 rather than 5.

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