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

With zero annotations, the description still covers the non-obvious behaviors: every list is re-verified with its RFC 5782 test entry so a dead zone reads as 'unavailable' rather than clean — a failure mode that materially changes interpretation. It also discloses no aggregate score, inclusion of delisting URLs, per-call pricing ($0.005 via x402/USDC) and the IPv4-only restriction.

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?

Front-loaded with the usage condition, then behavior, then cost — no filler sentences. The density is high but every clause (list count, raw codes, test-entry rechecks, delisting URL, price) carries decision-relevant 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 and no annotations, yet return values (per-list raw code plus published reason text), the delisting URL, and the dead-list degradation path are all described, so an agent can interpret results without extra calls. Minor gap: nothing on rate limits, concurrency behavior, or what an all-clean response looks like.

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 already 100% and the single parameter's IPv4-only constraint is documented in the schema itself. The description adds only the phrase 'one IPv4 address', which restates the schema rather than extending it — baseline 3 for a fully-covered single-param tool.

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 concrete verb and resource ('checks one IPv4 address against nine public DNS blocklists at once') and names the specific lists, which separates it from the generic red_ip lookup and the domain/email checks. The agent knows exactly what it gets back — raw per-list codes, not a verdict.

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 when an agent must decide whether an IP is already known for abuse' gives a clear triggering condition. It does not explicitly exclude neighbouring tools such as red_ip (reputation/geo lookup) or red_domain_check, so the routing to alternatives is left to inference rather than stated.

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