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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered elsewhere. The description adds genuinely new context by quantifying the check ('20+ major blacklists') and naming examples (Spamhaus, Barracuda, SORBS), which helps interpret results. It omits operational caveats such as query latency, RBL rate limits, or the possibility of false positives on shared IPs.

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?

One sentence, front-loaded with the action and scope, with the reported outcome trailing it. Every clause earns its place and nothing is padded.

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 single-parameter read-only check with no output schema and rich annotations, the description covers what is queried, against how many lists, and roughly what comes back. Only the absence of timing/rate-limit expectations and sibling disambiguation keeps it short of complete.

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% and there is a single required parameter whose schema text ('A domain or an IPv4 address') fully documents accepted input. The description restates the same domain/IP acceptance without adding format rules or edge cases such as IPv6 or subdomain handling, so 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?

The description gives a specific verb ('Check') and resource ('a domain or IP against 20+ major email blacklists') and explicitly states the output ('report which list it appears on'). It does not differentiate itself from close siblings such as check_surbl or check_domain_reputation, so an agent must infer the boundary rather than being told it.

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?

Usage is only implied: the wording suggests use when validating sending domains/IPs for deliverability or spam-listing problems, but there is no explicit when-to-use statement, no prerequisites, and no named alternative such as check_surbl. The agent can guess the context but is given no routing guidance.

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