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

Annotations already declare non-read-only, idempotent, non-destructive, so the safety profile is covered. The description adds real value with "from now on" (persistent, future-only effect) and "screened or not" (blocking applies regardless of screening state), but says nothing about reversibility, whether existing voicemail/missed-call history is affected, or required authorization.

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?

A single front-loaded sentence with no filler; both clauses carry information. It is arguably too terse given the missing routing and reversibility information, which is a completeness issue rather than a conciseness one.

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 only 2 fully documented params, annotations, and no output schema, the definition is workable but incomplete: an agent cannot tell from it how to reverse the block, whether it requires the secret or authentication, or how it interacts with allow. The "screened or not" clause partially compensates.

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%, documenting both secret and address with format examples. The description confirms the address identifies a caller to be refused but adds no syntax, format, or default details beyond the schema, so the baseline 3 applies.

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?

"Refuse a caller's calls" is a specific verb+resource that an agent can act on directly, and the effect is distinguishable from sibling tools like allow or let_in. It stops short of explicitly contrasting with those siblings, so a 4 rather than a 5.

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?

There is no statement of when to use this versus allow, let_in, or voicemail, and no mention of how a block is later undone. The only usage hint is the implied "from now on" persistence, which the agent must infer.

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