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

Annotations already cover safety (readOnlyHint, idempotentHint, destructiveHint=false), so the bar is lower; the description still adds genuinely useful context by naming the specific blacklist providers queried (an openWorld detail) and by promising removal links in the result. It omits latency/caching behavior and rate limits, which matters for a tool that fans out DNS lookups.

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?

A single front-loaded sentence that states action, accept-ed input modes, scope of query, and output payoff with no filler. Nothing could be cut without losing information.

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, yet the description tells the agent the result conveys listing status plus removal links, which is enough to know what comes back. With only one required parameter and full annotation coverage, the remaining gaps (multi-IP aggregation behavior, lookup latency) are minor rather than blocking.

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 the schema already documents the 'domain or IPv4' forms, but the description adds real meaning: for a domain it checks the domain's *sending IPs* (plural, implying MX resolution and fan-out), while the IPv4 path is a single-address check. That distinction is not in the schema.

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 gives a specific verb ('Check'), a specific resource (email blacklists), names the major lists queried (Spamhaus, Barracuda, SpamCop), and states both accepted target forms. This clearly separates it from the sibling DNS-authentication tools like check_spf, check_dmarc and check_mx.

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 description explains what the tool does but never says when to reach for it — e.g. before a cold-email send or after a deliverability drop — nor does it name an alternative such as check_cold_email or suggest_sending_domains. Usage is left entirely to inference.

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