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

With no annotations provided, the description carries the full behavioral burden and does so well: it discloses that sends to these addresses are stopped silently before leaving, with no bounce and nothing visible in the thread. That is exactly the non-obvious behavior an agent needs to avoid misdiagnosing a missing email.

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?

The description is front-loaded with the list's contents, then explains the silent-blocking behavior, then ends with the diagnostic use case. Three sentences, no repetition, and every sentence adds operational value.

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?

Given zero parameters, no output schema, and no annotations, the description is complete enough: it explains what the list contains (address, day, provider label), why it matters, and how suppression manifests to the user. An agent can select and correctly interpret this tool without further fields.

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?

The tool takes zero parameters, so there are no parameter semantics for the description to clarify. The baseline for a parameterless tool is 4, and no additional parameter guidance is needed.

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?

The description states a specific verb and resource: it lists addresses that marked this account's mail as spam and that the account can no longer write to. The spam-specific mechanism and the 'no longer write to' scope distinguish it from generic address-listing or blocked-sender tools.

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?

It gives a clear triggering scenario: read this list when a mail seems to have gone nowhere and nothing explained why. It does not explicitly contrast this with nearby tools such as list_blocked_senders or explain when suppression is not the right explanation, so it stops short of full alternative routing.

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