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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the safety profile is covered. The description adds genuinely useful semantics beyond that: rules affect future matching mail only, not already-received messages, and 'From is sender-controlled, not authenticated identity' is a meaningful trust caveat for interpreting results.

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 short sentences, each load-bearing: scope first, then the edit restriction, then the behavioral caveats. The UI path reference ('Account > Receiving rules') is slightly incidental but earns its place by redirecting the user.

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?

An output schema exists, so return values need not be described, and the annotations carry the safety profile. The description supplies the domain caveats an agent needs to interpret the rules correctly; only minor gaps (auth/error behavior) remain.

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 0% and the sole inbox_id parameter carries no description, but its name and UUID format make its meaning self-evident. The phrase 'this inbox's blocked senders' ties the parameter to the scoped resource, adding slight context without documenting format or error behavior.

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 ('Inspect') and a concrete resource ('this inbox's blocked senders'), so an agent knows exactly what it returns. It does not explicitly differentiate itself from the sibling get_sending_policy, relying on the name/title for that contrast, which keeps it just short of a 5.

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?

Tells the agent this is an inspection-only path: 'Only the human can edit them in Account > Receiving rules' makes clear the agent must not attempt modification and points the user where to go instead. There is no explicit naming of an alternative tool or a when-not condition tied to siblings, so it is clear context rather than full routing guidance.

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