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

Annotations already declare readOnly, idempotent, closed-world and non-destructive, so safety is covered. The description adds genuine behavioral value by disclosing the shape of the answer (points added, block-alone status, minimum plan tier), which the agent cannot infer from annotations. It does not discuss formatting or edge cases for unknown codes, keeping it below 5.

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 tight sentences, front-loaded with the core action, then the argument and the no-argument fallback. No filler; every clause carries 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?

There is no output schema, so the description carries the return-value burden and does so by enumerating the fields the agent will receive. Combined with full schema coverage on the single parameter and complete annotations, nothing needed to invoke or interpret the 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?

With one parameter at 100% schema coverage, the baseline is 3, but the description adds value by naming concrete example codes (disposable_domain, burner_mx, repeat_inbox, datacenter_ip) that illustrate the expected value domain, and reiterates the omit-to-list-all behavior meaningfully. It does not specify validation or error behavior for invalid codes.

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 (Explains) plus a specific resource (a SignupBouncer reason code), and enumerates the exact facts returned: meaning, point weight, whether it blocks alone, and lowest plan. This is clearly distinguishable from siblings like check_email and lookup_burner_domain, which perform lookups rather than explain codes.

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 defines the two operating modes: pass a code to explain one, or omit it to list every code. That covers the main branch an agent must decide. It stops short of contrasting against siblings (e.g. when to call lookup_burner_domain instead), so it is clear context without explicit exclusions.

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