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

Annotations already declare readOnlyHint/idempotentHint/destructiveHint=false, so the safety profile is covered. The description goes further by describing the shape of the explanation returned (meaning, points, blocking, lowest plan), which is valuable given there is no output schema.

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?

One tight sentence with no filler, front-loading the core action and then the returned fields, with the no-argument fallback trailing appropriately.

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 single-parameter, read-only explainer with no output schema, the description fully covers what is returned and the optional-code behavior. Nothing an agent needs to call it correctly 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?

Schema coverage is 100%, so the code parameter is already documented and the omit-to-list-all behavior is in the schema. The description nevertheless adds multiple concrete example codes (burner_mx, repeat_inbox, datacenter_ip) that help the agent recognize valid inputs.

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+resource ('Explains a signupbouncer reason code') and enumerates exactly what the answer contains: meaning, point weight, blocking behavior, and plan tier. This clearly separates it from siblings like check_email and lookup_burner_domain.

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 implies usage via the optional-code branch ('Without a code, lists every code'), which tells the agent how to invoke it in both modes. However, it never states when to reach for this tool versus lookup_burner_domain or check_email, leaving sibling routing to inference.

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