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 irreversibility warning ('It cannot be got back') largely restates structured data. The description adds no context beyond that, such as whether release is immediate, what happens to messages or assignments tied to the number, or any billing/verification impact.

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 with the destructive warning placed prominently rather than buried. The second sentence is partly redundant with destructiveHint but earns its place as an explicit irreversibility warning.

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 destructive, irreversible, single-parameter tool this is the minimum viable description. It covers the action and irreversibility but not timing, side effects on related resources, or what the response contains (no output schema exists to cover that instead).

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% and the single parameter is fully documented ('E.164 number you own'), so the schema carries the load. The description only echoes the ownership constraint and adds no format or validation detail beyond it.

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?

Specific verb + resource: 'Release a number you own' tells an agent exactly what is being acted on and that ownership is a precondition. It does not explicitly distinguish itself from near-siblings such as delete_number_pool or assign_number_to_customer, which is why it falls short of 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 alternatives, nor when not to use it. The only implied guidance is the ownership precondition embedded in 'a number you own'; nothing routes the agent between this and other number-lifecycle tools.

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