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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=true, so the bar is lower. The description usefully discloses the consequence of 'exclude' (the assistant will never reply to that number), which is real behavioral context beyond the annotations, but it says nothing about reversibility, permissions, or who is affected — meaningful gaps for a setting that silently changes reply behavior.

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?

One compact sentence covering both action values with no filler. The telegraphic phrasing ('exclude adds it...; not-internal dismisses...') is efficient, though the opening qualifier before the colon delays the actual verb.

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 3-parameter mutation with no output schema, the description covers the decision logic well but omits whether an exclusion can be undone and what happens if the number was already excluded. Annotations carry the safety profile, so the missing pieces are secondary rather than blocking.

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 only 33% (the 'action' and 'number' properties are bare), and the description compensates by explaining exactly what each action value means and where the number comes from. The 'brand' parameter is left entirely to the schema, which does document it with a get_overview slug reference, so the remaining gap is small.

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 the concrete effect of each action: 'exclude adds it to the numbers the assistant never replies to' and 'not-internal dismisses the suggestion'. It also anchors the input to the sibling tool list_internal_number_suggestions, so the resource and scope are unambiguous. It stops short of a clean verb+resource framing at the start, opening with a prepositional phrase instead.

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 tells the agent which of the two enumerated actions to pick and what each one does, and it identifies the upstream source of the number (list_internal_number_suggestions). It does not state when this tool should be used rather than simply ignoring a suggestion, nor any prerequisite like the assistant being paused or active.

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