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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world behavior. The description adds meaningful context beyond them: what the returned data represents (blocked senders/domains whose mail never arrives) and that mutation is a human-only action in a specific UI location. It does not describe return shape or pagination, but the output schema covers that.

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 short sentences, front-loaded with the tool's output and followed by the permission constraint. Every clause carries information; no filler or restatement of the title.

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 explained, and annotations cover the safety profile. The description supplies purpose, data meaning, and mutation constraints, leaving only minor gaps like result volume or ordering.

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 0%, so the schema only supplies a UUID pattern for inbox_id with no prose. The description's phrase 'from this inbox' implies the parameter scopes the policy to a single inbox but adds no format, sourcing, or lookup detail. With only one self-evident parameter, this is minimally adequate.

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 ('List') and resource ('senders and domains blocked from this inbox') and clarifies the consequence ('mail from them does not arrive'), which disambiguates it from the parallel get_sending_policy sibling by name alone. It never explicitly contrasts itself with get_sending_policy, so it stops short of the top score.

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 sentence 'Only the human can change them, in Account > Receiving rules' usefully tells the agent this is read-only and that no update tool exists for it, implicitly steering away from write attempts. It does not name an alternative tool or state when to prefer this over get_sending_policy, so guidance is implied rather than explicit.

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