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

With no annotations, the description carries the full burden. It clearly conveys that the tool returns a list of blocked addresses/domains, but it omits behavioral details such as whether the list is paginated, sorted, or includes both addresses and domains in a single response. For a trivial parameterless read, this is adequate but not thorough.

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 a single, front-loaded sentence with no wasted words. It names the action and the resource precisely, making it highly scannable for an agent.

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 zero-parameter, no-output-schema tool, the description gives enough context for an agent to know what the tool does and what it yields conceptually. It could be more complete by describing the shape of the returned list, but given the low complexity, the current description is largely sufficient.

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 has zero parameters and the schema has 100% coverage with an empty properties object, so there is nothing for the description to add about parameters. The baseline for zero-parameter tools is 4, and the description accurately reflects the no-input nature of the call.

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 uses a specific verb ('List') and a specific resource ('blocked sender addresses and domains for inbound email'), making the tool's purpose immediately clear. It also distinguishes itself from the sibling inbox_blocklist_add and inbox_blocklist_delete tools by focusing on listing rather than mutation.

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 the tool should be used when an agent needs to view currently blocked senders, and sibling names suggest add/delete as alternatives. However, it does not explicitly state when to prefer this tool over inbox_blocklist_add or inbox_blocklist_delete, or mention that it is a read-only operation.

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