Set Catch-All

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

Annotations already declare the write/idempotent/non-destructive profile, and the description adds meaningful consequence detail beyond them: `fail` bounces mail and `blackhole` silently discards it, which is exactly the operational risk an agent needs. It does not say that the setting replaces any existing catch-all configuration, which is the main residual gap.

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 sentences, zero filler, with the core behavior front-loaded and the conditional constraint placed second. Every clause carries information.

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?

With an output schema present and full parameter documentation, the description needs only to convey purpose and mode semantics, which it does. It is nearly complete; only the replace-existing-configuration behavior and permission expectations are left unstated.

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 100% and the schema already spells out both the enum meanings and the conditional requirement for `address`, so the description largely restates structured data. It adds no format or example detail beyond what the schema provides, making baseline 3 correct.

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 names a specific verb ('Sets') and resource ('how the domain handles mail addressed to nonexistent local parts') and then defines all three modes, so an agent immediately knows this is the write counterpart to get_catch_all in the sibling list.

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 the conditional rule for `address` (required for type `address`, omitted otherwise) which is real usage guidance, but it never states when to reach for this tool versus get_catch_all for reading the current configuration, and mentions no prerequisites or account permissions.

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