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

With no annotations, the description carries the full burden, and it does disclose one genuine behavioral trait: 'Sends to it are refused.' It omits reversibility (unblock exists), whether re-blocking an already-blocked address errors, permission requirements, and the response shape.

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 tight sentences, no filler, with the core action and its effect front-loaded. Nothing could be removed without losing 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?

For a mutation tool with no annotations, no output schema, and an undocumented 'reason' parameter, the description leaves too much open: no error behavior, no confirmation of what changes, and no pointer to unblock as the inverse. It covers the happy-path action only.

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 only 33%: 'kind' relies on its enum and 'reason' is entirely undocumented in both schema and description. The description's 'email address or a whole domain' merely restates the enum values and adds nothing about what 'reason' is for or how it is surfaced.

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 ('Block') and resource ('email address or a whole domain') with the scope 'for this account'. An agent can distinguish it from list_blocklist and unblock by the verb alone, though the description never names those siblings to make the routing explicit.

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?

No guidance on when to block versus alternatives such as add_unsubscribe or check_email, and no prerequisites (e.g., whether the address must be validated first). Usage is only inferable from the tool name and the sibling set.

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