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

Annotations already declare destructiveHint=true, idempotentHint=true and openWorldHint=true, so the mutation profile is covered. The description adds genuine business context not in the structured fields: the two-channel baseline and the fact that single extra channels are no longer sold, which constrains the operation to keep-or-lower. However, it never says what happens to in-progress conversations when the count is reduced, which is the key destructive risk the annotation flags.

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?

Three short sentences, front-loaded with the core purpose and no filler. The final clause is a bit convoluted ('Single extra channels are no longer sold, so this keeps or lowers an existing count') but it carries the most decision-relevant 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?

A two-parameter mutation with annotations covering safety and no output schema, so the bar is moderate. The description still leaves open the two things an agent most needs: whether the count can be raised via this tool, and what service impact lowering it has on live calls.

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 0%, so the description must compensate, and it partially does: 'The number includes 2' clarifies that channel_count is the resulting total (matching minimum 2), not an increment — an important disambiguation given the 'add_' name. number_id is not addressed at all, and no format or validation detail is offered.

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+resource: 'Sets how many simultaneous conversations a number can take.' An agent can tell this mutates a channel-count setting rather than buying a number or setting routing. It does not name siblings, and the verb 'Sets' sits awkwardly against the tool name 'add_number_channels', which sows a little doubt about whether the value is a total or an increment.

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?

'Single extra channels are no longer sold, so this keeps or lowers an existing count' implies a when-to-use boundary (retain or reduce, not grow), but it is phrased obliquely and never names what to call instead for adding capacity (e.g., buy_number/order_service). Usage is implied rather than stated.

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