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

Goes well beyond the readOnlyHint/idempotentHint annotations by disclosing that no query is performed, that a paid key would be required, and that the response content states nothing was checked. It even pre-describes the shape of the result (lookup URL plus alternative checks), which is unusually candid for a non-functional tool.

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, zero filler, and the most decision-relevant fact (it does not query) is front-loaded in the first clause. Every sentence earns its place.

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 compensates by describing what the response contains (a statement that nothing was checked, Spamhaus's lookup, and the checks the server does run). Nothing an agent needs to call or interpret this 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?

Single optional 'domain' parameter with 100% schema description coverage, so the baseline is 4. The description mentions the domain being asked about but adds no syntax or validation detail beyond the schema, which is acceptable at this coverage level.

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 ('Explains how to check a domain on the Spamhaus Domain Block List') and immediately disambiguates the title's 'not queried' caveat by declaring it never issues a listing verdict. An agent can distinguish it from check_surbl and check_blacklist without opening any 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?

Explicitly frames the manual path (https://check.spamhaus.org) and names the alternatives this server actually runs: check_surbl and check_blacklist. The when-not condition — no paid key, nothing is checked — is stated rather than inferred.

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