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

Annotations already declare readOnlyHint, openWorldHint, and idempotentHint, so the safety profile is covered. The description adds meaningful behavioral context by disclosing that the tool performs external checks (resolution, certificate, SURBL lookup, sharing detection) and explains why the tracking-domain listing matters to content filters. It does not mention latency, rate limits, or failure behavior, but it goes beyond the annotations.

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?

The description is two sentences and front-loaded with the concrete checks, which is efficient. The second sentence, about content filters hashing the tracking domain, is useful rationale but is not strictly necessary for correct invocation, keeping this just below a perfect score.

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 composite multi-check tool with no output schema, the description does well to enumerate the checks but does not describe the shape of the result — whether each check is a boolean, a multi-field report, or a status summary. An agent knows what will be examined but not what it will get back, which is a notable gap given the absent output schema.

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%, so both parameters, including the optional sendingDomain, are already fully documented in the schema. The description's phrase 'belongs under the sending domain' reinforces the purpose of sendingDomain but does not add syntax, format, or behavior beyond what the schema already provides, so the 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 uses a specific verb and resource — checking a campaign's click-tracking domain — and enumerates exactly what is checked: resolution, certificate, SURBL list, listed address, sending-domain relationship, and shared tracking host. This composite scope clearly distinguishes it from single-purpose siblings like check_surbl, check_ssl, and check_dns without naming them.

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 implied by the phrase 'a campaign's tracked links,' which tells an agent the context in which to reach for this tool. However, there is no explicit when-to-use/when-not guidance and no routing advice versus the many overlapping sibling checks (check_ssl, check_surbl, check_dns, check_blacklist).

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