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

Annotations already declare readOnlyHint, idempotentHint and non-destructive, so the safety profile is covered. The description adds real value beyond them by disclosing the return shape — a weighted A-F score, per-check breakdown, and remediation guidance — which no output schema provides here. It does not mention lookup latency or which blacklists are consulted, keeping it at a 4.

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?

Three short sentences with zero waste: capability first, return content second, entry-condition last. Every sentence carries distinct information an agent needs.

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 one-parameter, read-only tool with no output schema, the description covers what is checked, what comes back (weighted score, per-check breakdown, fixes), and when to reach for it. Nothing an agent needs to invoke it correctly 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?

There is a single parameter with 100% schema description coverage, and the schema already clarifies "Not an email address" with an example. The description adds no additional parameter meaning, so 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 and resource ("Grade a domain A-F") plus the domain of concern (cold email readiness), then enumerates exactly what is inspected. The phrase "checks SPF, DKIM, DMARC, MX, blacklists and domain age together" implicitly separates it from the many single-check siblings (check_spf, check_dmarc, check_blacklist) without opening a schema.

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?

"Start here for open-ended 'is this domain any good' questions" gives a clear entry condition that selects this tool over the granular per-record checks. It stops short of an explicit when-not clause (e.g., 'if you already know which record failed, use check_spf'), so it is strong context without full routing.

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