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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false. The description restates the read-only safety and adds the 'company-wide blacklist' scope, but it does not disclose meaningful additional behavioral details beyond what the annotations already provide.

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 short, front-loaded sentences state the core action first, then give a compact safety/usage note. There is no filler or unnecessary repetition.

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 simple, read-only blacklist check, the description provides the purpose, input categories, and usage moment. The main gaps are the lack of an explicit return shape and no mention of multiple/zero-parameter behavior, but those are minor for this kind of Boolean-style check.

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 coverage is 100%, with each parameter already described, so the description only needs to add contextual meaning. It reinforces that domain/company/contact_id are check targets, but it does not clarify precedence or behavior when multiple or zero optional parameters are supplied.

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 precise action ('Check whether ... matches') and a clear resource scope ('authenticated user's company-wide blacklist'). It covers the three input categories from the schema and is easily distinguished from the sibling list_blacklist tool.

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 explicitly identifies a workflow moment: 'safe to call before adding a lead to a campaign.' It does not, however, name alternatives such as list_blacklist or specify when not to use it, so it falls short of a full 5.

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