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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint), so the external-network nature is declared. The description adds that the check spans multiple "major" blocklists and returns per-list results, which is useful context, but it does not say which lists are queried, whether results are cached/authoritative, or how many lists to expect.

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?

Two sentences, no filler, and the usage trigger is front-loaded ahead of the mechanics. Every clause earns its place by either telling the agent when to call the tool or what it produces.

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 lookup with no output schema, the description supplies the trigger condition, the mechanism, and a one-line return summary. It stops short of describing the response fields or what a partial/error result looks like, but nothing essential to correct invocation 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 description coverage is 100% and the single parameter is fully documented with examples ("example.com or 1.2.3.4"), so the schema carries the load. The description adds no syntax or format detail beyond what is already in the schema, making 3 the correct baseline.

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 ("Checks the domain against major DNS blocklists") and even summarizes the return shape ("returns the result for each list"). It implicitly distinguishes itself from DNS-record siblings like spf_check or mx_lookup by naming blocklists, but it never names an alternative explicitly, so an agent must infer the boundary.

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?

"Use this when the user suspects their domain is blacklisted or blocked" gives a concrete triggering condition rather than a vague hint. There are no exclusions or named alternatives, however, so an agent facing a general "is my email setup healthy?" request gets no routing help among the many sibling check tools.

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