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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so the safety profile is covered. The description adds real domain context about what SURBL evaluates (body-embedded domains) and restates the 100-domain batch cap, though it says nothing about the shape of the result (per-domain verdicts, which list was hit).

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?

Three tight sentences: the action and scope lead, the explanatory rationale follows, and the limit closes. No filler and nothing that doesn't help an agent decide or call.

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 batch lookup with rich annotations, the definition covers what to send and why it matters. The remaining gap is the absent output schema combined with no description of what a result looks like, which slightly weakens an otherwise complete definition.

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?

There is a single parameter with 100% schema description coverage ('Domains to check. Max 100.'), so the schema already does the work and the baseline is 3. The description repeats the 100-domain cap without adding format guidance (bare domains vs. URLs, whether subdomains count).

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 (check), a specific resource (domains against the SURBL URI blacklist) and the batch scope. That clearly separates it from siblings like check_blacklist, check_domain_reputation and check_tracking_domain, which are domain/IP reputation tools rather than a URI-body blacklist.

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?

The description supplies the decision context an agent needs: URI blacklists cover domains inside a message body, and a single listed tracking/landing domain sinks the whole email regardless of sender reputation. That is a clear when-to-use signal, but it names no alternatives or exclusions (e.g., when to prefer check_tracking_domain or check_blacklist).

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