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

Annotations already declare destructiveHint=true, idempotentHint=false, and openWorldHint=true, so the safety profile is covered. The description adds the non-obvious billing behavior (monthly charge for live numbers) but says nothing about irreversibility, whether the number is immediately active, or that release_number is the undo path.

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 sentences, zero filler, with the primary action stated first and the cost caveat second. Every clause carries information an agent can act on.

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, open-world purchase with no output schema, the description should say what comes back (the number record/id) and what happens on failure or when the number is unavailable. Billing is covered, but the outcome shape and irreversibility are left to inference.

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 75% and the schema already documents customer_id, idempotency_key, and registration_id in detail. The description's sandbox/live framing loosely aligns with the registration_id note but adds no new parameter-level meaning. 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?

States a specific verb and resource ("Buy a phone number for your account") and clarifies the sandbox-vs-live distinction. It does not, however, name the adjacent siblings (search_available_numbers, bulk_purchase_numbers, assign_number_to_customer) that an agent must choose between.

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?

The parenthetical about free sandbox numbers with test keys and the note that live numbers are billed monthly give real decision context (cost implication of going live). But there is no explicit when-to-use/when-not, and no routing to bulk_purchase_numbers for multiple numbers or search_available_numbers to find a purchasable number first.

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